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ATTENBOROUGH: The natural world
is full of extraordinary animals

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with amazing life histories.

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Yet certain stories
are more intriguing than most.

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The mysteries
of a butterfly's life cycle

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or the strange biology
of the emperor penguin.

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some of these creatures were surrounded
by myths and misunderstandings

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for a very long time.

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And some have only
recently revealed their secrets.

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These are the animals
that stand out from the crowd.

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The curiosities 1 find
most fascinating of all.

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ATTENBOROUGH: The abilities
of some plants and animals

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are so remarkable that they
seem to be almost supernatural.

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1n this programme,

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1 investigate the shocking
power of a fish

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that advanced our
understanding of electricity.

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And plants with senses
that are surprising modern science.

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But how did these extraordinary powers
help the organisms that produce them?

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The freshwater eel
is surrounded by legends.

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The first Europeans
to explore the New World

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heard amazing stories about it.

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And when, in the 1 8th century, specimens
of this strange fish reached Europe,

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they created a sensation.

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In 1 776, Captain George Baker,

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an American mariner and whaler,

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made the long and difficult
journey from South America,

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across a raging Atlantic Ocean,

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to bring five,
live electric eels to London.

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These are two of his actual eels.

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Captain Baker and his five electric
eels, or Gymnotus, as they were known,

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set up shop in the Haymarket

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and offered two shillings
and sixpence for a shock

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or five shillings for a spark.

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Baker's eels had come all the way

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from the lower reaches
of the Amazon and Orinoco rivers

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where he had heard tales from the locals

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about their astonishing powers.

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They called these fish ''trembladores''.

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Humboldt, the famous naturalist
and explorer,

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had described how
he had witnessed horses

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being killed by the repeated
shocks from these fish.

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And he himself accidentally
stepped on one

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and vividly described the effect.

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''With each stroke
you feel an internal vibration

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''that lasts two or three seconds
followed by a painful numbness.

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''All day, 1 felt strong pain in my knees
and in all my joints. ''

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I encountered this remarkable fish
in its natural environment

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where I filmed at the same rivers

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that Humboldt explored.

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There was talk of me
swimming with the eel,

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but, thankfully, we had
some technical difficulties

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with the diving equipment
that I was supposed to wear.

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And so I stayed safely in the canoe

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and was able to demonstrate
another subtler

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but equally remarkable side
to this fish.

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The eels were constantly
producing electric discharges.

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somehow, they were generating
a small, nonstop flowing current.

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(DEVICE BUZZING)

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They were also able to sense electricity

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and were attracted to electrical pulses

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emitted from my underwater detector,

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suggesting that electricity
plays a key role in their lives.

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But at the time of their discovery,

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no one knew the full functions
of their extraordinary abilities.

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We know now that the shock
was caused by electricity.

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And I can demonstrate it by
touching the animal with an electrode.

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Watch.

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There, you see?

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The scope in the lights
are flashing up and down.

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Extraordinary.

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But this is only a small indication
of the real power of this fish.

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If I were to try and pick it up,

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I could get a jolt
of an astonishing 600 volts,

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which is quite enough to kill me.

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This 1 960s educational film
illustrated the shock

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even though the equipment
used prevented the volunteers

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from getting its full power.

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They were to join hands
and then connected to a live eel.

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(VOLUNTEERS EXCLAIM IN SURPRISE)

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Ah.

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Firm believers in electric eels.

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Thank you very much.

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You can imagine how startling Baker's
electric eels were 200 years ago.

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In the 1 8th century,

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electricity was becoming one of
the most fashionable areas

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of scientific investigation,
but it was still very poorly understood.

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Very few advances had been made
since its discovery 1 50 years earlier

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by Elizabeth I's personal physician,
William Gilbert.

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Gilbert repeated a trick that had
been known about since Greek times.

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Rubbing a piece of amber with cat fur

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that allowed the amber to attract
a small object, like a feather.

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Let's give it a try.
Here's a bit of amber.

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There.

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It has always been assumed

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that this amber effect
was caused by magnetism,

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but Gilbert showed
that it was something different.

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He named this new force after
the Greek word for amber, electron,

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and so electricity was born.

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Londoners of the time developed
a fascination for this magical force.

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showmen staged bizarre spectacles
to demonstrate its properties.

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1n one, a young boy attached
to a friction generator

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attracted small pieces
of paper to his hands.

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1n another, a gentleman kissed a lady
and was repulsed by the charge

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carried through her whalebone corset.

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No one knew what to do with electricity,

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but a better understanding of
its nature was slowly emerging.

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More and more ingenious ways
were developed

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to create what we now call
''static electricity''.

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And soon, it became something more
than just a quirk of rubbing amber,

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it became visible as a spark.

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-(ZAPPING)
-Ooh. (CHUCKLES)

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The ability to produce
this characteristic blue spark,

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along with its invigorating smell,
became the signature of this new force.

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And it prompted scientists
to make obvious comparisons

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with other natural phenomena.

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(THUNDER RUMBLING)

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1n the American colonies,

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Benjamin Franklin bravely, or perhaps
foolishly, flew kites into thunderstorms

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and proved that lightning
and the electric spark

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were one and the same.

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But there's another common property
of lightning and static electricity,

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that is the ability to shock.

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It wasn't long before a comparison

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was made between the shock
from the early generators

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and the shock that could be
delivered by a fish.

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The electric eel
wasn't the only kind of fish

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known to give humans a powerful jolt.

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The ancient Egyptians
knew that the electric catfish

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could also give shocks and they
called it the ''Thunderer of the Nile''.

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And in the nearby Mediterranean
lives the torpedo ray.

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1ts muscle batteries make it so bulky,

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it can't undulate its body
like other rays,

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but has to propel itself
by waving its tail.

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Like the electric eel,

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it uses its discharge to stun
the other fish on which it preys.

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Sadly, the pressure of celebrity

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and having to produce shocks
and sparks to order

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exhausted Baker's long-suffering eels
and they didn't last the winter.

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But two were preserved
and expertly dissected by john Hunter,

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a very distinguished
Scottish surgeon of the time.

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And he found a great number
of striped muscular layers

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that proved to be where
the electricity was generated.

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They're now referred to
as ''Hunter's organs''.

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He found these muscles along the tail

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and sides of the eels
arranged in stacks.

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One scientist called Galvani

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believed that animals had
their own natural electricity

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even without these electric organs.

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And he tried to prove this by
connecting wires to frogs' legs

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and making them twitch.

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He called this phenomenon
''animal electricity''.

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But another scientist
called Volta had other ideas.

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He proved that the frog was

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merely a conductor for electricity
with a simple experiment.

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Volta replaced Galvani's frog

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with discs of cloth soaked
in saltwater or acid

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and sandwiched them
between two different metals.

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I can do the same thing
with filter paper,

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copper two pence pieces

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and these simple
galvanised zinc washers.

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Watch.

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Tuppenny piece,

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filter,

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and washer.

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There. Nearly 0.6 of a volt.

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But the amount of electricity
he generated was tiny,

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certainly not enough to make
the spark seen from eels.

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Unlike Galvani,

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Volta saw no distinction
between animal electricity

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and his new electricity from metals.

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So, he now looked to animals

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to see how he might amplify
his new device.

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Was it significant

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that the muscles producing
the electric power in the eels

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were arranged in stacks?

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Volta decided to add more stacks
to his electric pile.

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We call this way of connecting
electric cells together ''in series''

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and we now know
that it increases the voltage.

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But Volta was about to find
this out for the first time.

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He piled up his tiny cells

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like the bands of muscle
in an electric fish.

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Here, I've got 1 0 pairs and just watch.

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Nearly six volts.

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Wonderful.

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Volta could now produce heat, shocks,

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and even sparks from electricity
in a continuous, never-ending stream.

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He had made the first battery,
partly inspired by the electric eel.

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The pieces of the puzzle
had come together

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and the eel's example had helped

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to advance our understanding
of electricity.

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Eels, in fact,
contain natural batteries,

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stacks of special muscles.

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It's amazing to think when electricity
is so much a part of our lives today

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that, before Volta, the only source
of electricity was lightning,

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a few static generators and fish
like this incredible electric eel.

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Understanding how electric eels
manage to find their way around

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revealed a hitherto
unknown animal sense.

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But it's not just animals
that have surprised us.

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We're now discovering that plants, too,

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have intriguing abilities
that are still mysterious.

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We think of plants as passive, still,
and silent,

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but they may have more in common
with animals than you might think.

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New research suggests that they
have surprising abilities.

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It depends on how you look at them.

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1 first started seeing plants
in a different light

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when making a series called
The Private Life of Plants.

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We used time-lapse photography
to reveal the way they move.

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The bramble spreads aggressively,
seemingly unstoppable.

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Other plants pulse
to the rhythms of day and night

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and flower buds explode like fireworks.

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so with speeded-up film,

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we've been able to translate
their time into ours,

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and to realise that they're
constantly on their move.

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Two hundred years ago, one plant
that moved very quickly indeed

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attracted the attention
of a great scientific mind.

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1t appeared to behave like an animal

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and could move fast enough
to catch its own food.

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Charles Darwin was fascinated
by the Venus flytrap.

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He called it ''one of the most
wonderful plants in the world''.

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He recognised that it could
move in a very different way

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to that of plant growth.

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This movement was not only fast
but also repeatable.

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Darwin experimented and found that

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the traps were not
triggered by raindrops,

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but only by a very particular
stimulation of the leaf hairs,

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such as an insect might make.

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But what intrigued him most
was the speed of the reaction.

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He sent one of these flytraps
to a friend,

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Dr Burdon-Sanderson, who was
performing groundbreaking work

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on muscles and electricity.

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His tests confirmed that
the tiny, electrical discharge

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caused by an animal muscle
cell contracting

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was almost identical to those signals

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obtained by attaching electrodes to
the flytrap when it was shutting.

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Although plants have no muscles,

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electrical stimulation enables them
to move in a similar way to animals.

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Electrical signals cause cells
to change the pressure

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of sap in their leaves,
so creating movement.

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As a result, some plants, like animals,
can actively catch their prey.

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Recently, it's been discovered
that other plants use electricity too,

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but for a very different purpose.

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Plants are rooted to the ground
and have a small, negative charge.

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The higher up the plant you go,
the greater the electric charge.

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This creates an electric field
around the flower.

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We can't see it, but these electrodes
are picking up...

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-(DEVICE HUMMING)
-The energy of this tiny field

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00:15:19,807 --> 00:15:23,516
and converting it into the sound
that we can hear.

247
00:15:23,607 --> 00:15:27,361
Bees, on the other hand,
have a positive charge.

248
00:15:27,447 --> 00:15:30,803
Friction whilst flying causes
them to lose electrons,

249
00:15:30,887 --> 00:15:32,843
leaving them electrically charged.

250
00:15:33,807 --> 00:15:35,798
As a bee approaches a flower,

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00:15:35,887 --> 00:15:37,878
the charge fields around the flower

252
00:15:37,967 --> 00:15:39,639
-and the bee interact...
-(WHINING CHANGES FREQUENCY)

253
00:15:39,727 --> 00:15:41,001
And the sound changes.

254
00:15:41,807 --> 00:15:43,286
There.

255
00:15:43,367 --> 00:15:46,757
And when it lands,
the positive and negative fields

256
00:15:46,847 --> 00:15:49,315
immediately cancel each other out.

257
00:15:49,407 --> 00:15:53,116
As this happens, there are two
very surprising consequences.

258
00:15:53,207 --> 00:15:56,756
Firstly, the plant's
negatively-charged pollen

259
00:15:56,847 --> 00:16:01,682
actually jumps across
onto the positively-charged bee.

260
00:16:01,767 --> 00:16:05,521
Secondly, the plant
has a changed electrical field.

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00:16:05,607 --> 00:16:07,643
And when another bee comes along,

262
00:16:07,727 --> 00:16:10,799
it detects this altered
electrical signature

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00:16:10,887 --> 00:16:12,366
and avoids the flower.

264
00:16:12,447 --> 00:16:15,120
The plant is, in effect, telling the bee

265
00:16:15,207 --> 00:16:18,199
that it has no nectar
and to come back later.

266
00:16:20,247 --> 00:16:23,364
When the flower has refilled
its stores of nectar,

267
00:16:23,447 --> 00:16:26,086
it creates a new electric charge

268
00:16:26,167 --> 00:16:29,000
which attracts another passing bee.

269
00:16:29,087 --> 00:16:34,400
This simple on/off signal
benefits both the bee and the flower,

270
00:16:34,487 --> 00:16:37,559
but it does have its limitations.

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00:16:37,647 --> 00:16:39,444
The electrical field is tiny

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00:16:39,527 --> 00:16:42,883
so insects can only
detect it at close quarters.

273
00:16:44,407 --> 00:16:45,806
But flowers can also

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00:16:45,887 --> 00:16:49,197
draw attention to themselves
over much greater distances

275
00:16:49,287 --> 00:16:52,563
and they do this
by floating messages in the air.

276
00:16:54,567 --> 00:16:57,957
The perfume of a flower
is not just a pleasant smell,

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00:16:58,047 --> 00:16:59,924
it's also the primary way

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00:17:00,007 --> 00:17:02,362
in which plants
communicate with insects.

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00:17:02,447 --> 00:17:06,235
A rose can contain
over 400 chemical compounds

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00:17:06,327 --> 00:17:11,959
and the bee can recognise a particular
combination from over a mile away.

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00:17:12,047 --> 00:17:15,323
Very latest research
has discovered that 90%

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00:17:15,407 --> 00:17:20,083
of the chemicals made by plants
are also produced by insects.

283
00:17:20,167 --> 00:17:22,237
And that is no coincidence.

284
00:17:25,287 --> 00:17:30,486
Most flowers produce scent to
persuade insects to visit them,

285
00:17:30,567 --> 00:17:34,355
but others use it
in a more sophisticated way.

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00:17:34,447 --> 00:17:36,403
For protection.

287
00:17:37,087 --> 00:17:41,285
Cabbages communicate
with each other using smell.

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00:17:42,567 --> 00:17:45,798
When the leaves of one plant are
being attacked by caterpillars,

289
00:17:45,887 --> 00:17:49,960
it releases a scent
which warns its neighbours.

290
00:17:50,047 --> 00:17:52,686
They then produce chemicals
in their leaves

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00:17:52,767 --> 00:17:56,601
that caterpillars don't like
and so they avoid being eaten.

292
00:17:57,607 --> 00:18:01,919
And scent also serves to call
in the cavalry.

293
00:18:02,007 --> 00:18:06,080
Leaves that are under attack give off
a chemical alarm signal

294
00:18:06,167 --> 00:18:11,639
that attracts wasps, which obligingly
pick off the caterpillar attackers.

295
00:18:14,567 --> 00:18:18,196
so, vegetables, fruits,
leaves and flowers

296
00:18:18,287 --> 00:18:22,041
are constantly communicating
with each other using touch,

297
00:18:22,127 --> 00:18:24,516
vision and smell.

298
00:18:24,607 --> 00:18:30,398
They seem to exploit all the senses
apart, that is, from hearing.

299
00:18:30,487 --> 00:18:33,797
But there are old stories
that one particular plant

300
00:18:33,887 --> 00:18:37,436
is able to produce a very strange sound.

301
00:18:38,647 --> 00:18:40,239
Hundreds of years ago,

302
00:18:40,327 --> 00:18:42,841
a plant with a root
that was thought to resemble

303
00:18:42,927 --> 00:18:47,876
a human body was said
to emit a sound that could kill.

304
00:18:47,967 --> 00:18:50,162
The root was known to
have strong anaesthetic

305
00:18:50,247 --> 00:18:52,044
and hallucinogenic properties

306
00:18:52,127 --> 00:18:54,004
and, in the 1 st century AD,

307
00:18:54,087 --> 00:18:58,842
it was called a ''mandroga''
or ''mandrake'' as it's now known.

308
00:18:58,927 --> 00:19:02,203
It was associated with magic
and the supernatural

309
00:19:02,287 --> 00:19:04,118
and was thought to derive power

310
00:19:04,207 --> 00:19:07,756
from a demon that emitted
a dreadful and fatal shriek

311
00:19:07,847 --> 00:19:09,724
if the plant was uprooted.

312
00:19:10,327 --> 00:19:15,526
Fortunately, there were creative ways of
avoiding death from the killer sound.

313
00:19:15,607 --> 00:19:18,326
One account advised plugging one's ears

314
00:19:18,407 --> 00:19:22,923
and then tying a starving dog
to the mandrake plant.

315
00:19:23,007 --> 00:19:25,521
And then, as the dog lunged for food,

316
00:19:25,607 --> 00:19:27,962
the plant would be uprooted.

317
00:19:28,047 --> 00:19:31,039
The dog would tragically die
from the mandrake's shriek,

318
00:19:31,127 --> 00:19:33,357
but the man would survive.

319
00:19:35,887 --> 00:19:38,321
This particular story may have arisen

320
00:19:38,407 --> 00:19:43,800
because drinks made with the mandrake
root can produce hallucinations.

321
00:19:47,127 --> 00:19:51,484
But we're just beginning to realise
that the sensory abilities of a root

322
00:19:51,567 --> 00:19:54,843
could be as sophisticated
as the rest of the plant.

323
00:20:00,127 --> 00:20:04,086
Latest research suggests that
roots are communicating underground.

324
00:20:06,727 --> 00:20:13,724
And we now have the technology
to eavesdrop on the roots' world.

325
00:20:13,807 --> 00:20:20,804
Believe it or not, the roots of these
corn seedlings can make and sense sound.

326
00:20:20,887 --> 00:20:25,165
The noise is very quiet,
but we can hear it with this equipment.

327
00:20:26,047 --> 00:20:30,245
If I place a corn seedling
in front of a laser beam like this.

328
00:20:34,967 --> 00:20:40,644
Now, the sound vibration can be detected
and we can hear it through a speaker.

329
00:20:41,167 --> 00:20:43,203
(CRACKLING)

330
00:20:43,287 --> 00:20:44,686
There.

331
00:20:44,767 --> 00:20:49,397
That strange crackling is
the sound of corn roots growing.

332
00:20:49,487 --> 00:20:52,445
It can be seen as pulses on the screen.

333
00:20:52,527 --> 00:20:55,883
It's been shown, too,
that the corn roots respond to the sound

334
00:20:55,967 --> 00:20:58,162
when it's played back to them.

335
00:20:58,247 --> 00:21:00,920
Time-lapse footage shot
over just a few hours

336
00:21:01,007 --> 00:21:06,639
clearly shows the roots growing towards
the tiny speakers that emit the sound.

337
00:21:06,727 --> 00:21:11,164
There's much speculation about
the purpose of this curious phenomenon.

338
00:21:11,247 --> 00:21:15,126
Perhaps, it helps roots
avoid growing into hard objects

339
00:21:15,207 --> 00:21:18,404
or being too close to competing plants.

340
00:21:18,487 --> 00:21:21,957
It could act like simple echolocation.

341
00:21:22,047 --> 00:21:25,164
We just don't know,
but it's the first clear evidence

342
00:21:25,247 --> 00:21:28,557
that plants have
a rudimentary form of hearing

343
00:21:28,647 --> 00:21:32,925
and might even be communicating
underground using sound.

344
00:21:33,007 --> 00:21:35,680
Sensitive equipment
is creating a new window

345
00:21:35,767 --> 00:21:38,918
into the plant world
and it seems that, like animals,

346
00:21:39,007 --> 00:21:41,999
they have a sophisticated sense
of their environment

347
00:21:42,087 --> 00:21:44,885
and possessed abilities
that not so long ago,

348
00:21:44,967 --> 00:21:48,403
we would have thought
of as supernatural.