All language subtitles for David.Attenboroughs.Natural.Curiosities.Series.3.3of6.Expandable.Bodies.720p.HDTV.x264.AAC.MVGroup.org

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The natural world is
full of extraordinary

animals, with amazing
life histories.

Yet, certain stories are
more intriguing than most.

The mysteries of a
butterfly's life cycle,

or the strange biology
of the Emperor penguin.

Some of these creatures
were surrounded by myth

and misunderstandings,
for a very long time.

And some, have only recently
revealed their secrets.

These are the animals, that
stand out from the crowd,

The curiosities, I find
particularly fascinating.

The bodies of some animals, stretch
and shrink in extraordinary ways.

Constrictor snakes, can swallow
prey, twice their own size.

While the camel's hump can
almost double in weight,

giving it the energy to travel
huge distances across deserts.

What is the secret behind
such expandable bodies ?

We've long been fascinated,
by the camel's

Places where,
during summer,

temperatures can sore, up
to 50 degrees Celsius,

while in winter, they can drop,
to 30 degrees below freezing.

With little in the way of
food or water, camels can

sometimes go without eating
or drinking, for over a week.

Most other animals, couldn't
survive conditions like this.

How does the camel do it ?

The camel's secret, was
thought, to lie in its hump.

In a healthy camel, it can be
big and firm, like this one,

and can weigh as much as 30 kilos,
which is the weight of a 10-yo child.

But if the camel goes without
food, and particularly

water, for any length of time,
then the hump can get floppy

and even droop over on one
side, as that one has done.

So people used to think, that the
camel stored water in its hump.

In fact, there are two
different kinds of camel.

The one-humped, or Dromedary

and the two-humped, or Bactrian.

Nearly all camels
alive today, are the

domesticated descendants
of one or the other.

The wild Dromedary almost
certainly, doesn't exist.

And only a few Bactrian camels remain,

roaming the deserts
of Central Asia.

A camel is a very tough animal,

but in the wild today,

it's rarer than the Giant Panda.

It's hard to say, where the idea

of a water-storing
hump came from.

The ancient Romans, were
the first to suggest,

that the camel may have a
built-in water reservoir.

And then, later on,
people got the idea,

that it had two stomachs.

One for food, and one for water.

In the 18th century, an eminent
anatomist, John Hunter,

decided to investigate the
truth behind these assertions,

and he dissected a camel.

He found, that the stomach
consisted of 3 or 4

compartments, similar to
those of a cow or a sheep.

But inside one of
those compartments,

he discovered these
pocket-like structures,

which are not found, in
any other large mammal.

Hunter didn't know what
the pockets were for,

but others after him, proposed

that they were special,
water-storing cells.

And then, despite any kind of
evidence to prove that this was true,

for another 250 years, books on
natural history, like this one,

featured illustrations of water-storing
cells, in the camel's stomach.

We now know, that
that's not true,

even though, we don't know exactly,
what the strange pockets are for.

But, the camel's hump is
certainly not filled with water.

It's made entirely
of fatty tissue.

It is, in fact, an
energy reserve,

for times when food is scarce.

And it can expand
to such a degree,

that it makes up 80 percent
of the camel's body-fat.

This enables a camel
to go for two weeks

without feeding, if necessary.

But there's a twist
to the story.

When fat is broken down
in the body, it produces

not just energy, but also water.

In fact, each gram of
fat broken down during

metabolism, produces
one gram of water.

So, could the camel's hump provide
it with extra water, after all?

A fatty hump, that contains
both food and water

would seem to be just what
a desert animal needs.

But, it's not as simple as that.

To consume its fat, an
animal needs more oxygen,

so, it has to breathe more.

So, when living on the fat in
its hump, the camel actually

looses more water through
its airways, then it gains.

So the camel doesn't have
a secret store of water.

How then, can it survive
in a waterless desert?

Camels can go without drinking,
for more than a week,

because they have an
extraordinary ability,

to retain the body moisture.

We ourselves, loose over
a liter of water a day,

through our
moister-laden breath.

But the camel has nostrils,
which he can shut tight.

And that, not only
keeps out the sand,

but retains the breath,
within the nose.

And there, the moisture
can be reabsorbed

by the linings of the nostrils.

Most mammals also
loose a lot of water,

when they cool their
bodies, by sweating.

But camels can endure a
rise in body temperature,

that would kill
most other mammals.

Without sweating.

If our temperature goes up,
by as little as one degree,

it's a sign of illness.

While 3 degrees causes vital organ
damage, and eventually death.

The camel can cope with as much as
6 degrees rise, with no ill effect.

This means, that camels
don't have to sweat,

until conditions get
very hot, indeed.

And, if necessary,
they tolerate loosing

more of their body water,
than other mammals.

When animals become dehydrated,

their blood becomes thicker, and more
difficult to pump through the body.

If we loose 10 percent
of our body water,

we start to go dizzy and blind.

And at 15 percent, our
internal organs start to fail.

Camels however, can loose a third of
their body water, with no ill effect.

Something that would
kill most other animals.

How do they do it?

Well, some of the answers may lie
in the shape of their blood cells.

These are the red blood cells
from a human being,

which are disc-shaped,
like that of most mammals.

These, on the other
hand, are from a camel,

and are slimmer and
more oval in shape.

It may be, that the oval,
streamlined shape,

makes it easier for
the blood to flow,

when the animal is dehydrated.

Certainly, the camel's blood is
less thick and sticky than ours.

The cells also have
particularly strong walls.

This prevents them from
rupturing, when the

animal suddenly drinks
large amounts of water.

And when they do find water,

camels have the ability,
to drink it very quickly.

A single camel, can
take the contents

of all these bottles,
(that's 100 liters),

in a mere ten minutes.

For any other animal to do that,
it would be extremely dangerous.

But the camel has the ability,to
hold the water in the stomach,

and only release it
into the blood stream,

very slowly, in a way
that does no damage.

We now understand, how camels can
survive harsh desert conditions.

And yet, surprisingly,
new research suggests,

that they may first
have evolved,

to live in the cold Arctic.

Scientists, have
recently discovered

the fossil bones of
giant, shaggy camels,

that roamed the forests
of the Canadian Arctic,

something of a half
million years ago.

The arctic camel was a third
larger, than the modern Bactrian

but otherwise looked
very similar.

And that may be no coincidence.

The wide, flat feet,
that stop the camel

from sinking into desert sand,

could also have helped its
ancestors, walk in deep snow.

And a fatty hump,
provided the food reserve

the camel would need, to
survive long, cold winters.

We may never fully understand the
mysteries of the camel's hump,

but it evolved first, as a way of
keeping warm, or staying cool.

But we have unraveled
many other mysteries,

of the animal's body,
that enable it

to endure conditions,
that few other

animals would be
able to withstand.

The camel's hump can change
dramatically in shape and size.

And in part two, we
meet another creature

that can stretch its body,
in a most extraordinary way.

The camel can go for
days, without water.

Our second curiosity, can
fast for months on end,

and then devour prey,
many times its own size.

This is a green Anaconda.

One of the largest
snakes in the world.

It's about 4 meters long,
and weighs 70 kilos.

And it's only half grown.

They can grow to a
length of 6 meters,

and weigh twice as
much as this one.

But it's their ability to
be able to swallow

enormous prey, that's really
grabbed our imagination.

Could one of these
really bite a man,

and swallow him
whole, and alive?

In the 16th century,

European explorers, venturing
into the Amazon jungle,

were fascinated by tales
of a huge river monster.

It was said to devour
cattle and deer

and to spit out water,
like shot from a canon

knocking animals out of trees.

These fantastic
stories, led people

to go in search of
this marvelous beast.

In 1907, a British explorer,
Colonel Percy Fawcett,

claimed to have encountered

an enormous snake,
on the Amazon river.

"A huge head", he said,
rose up from the water,

dangerously close to his canoe,

and a colossal anaconda emerged.

Greatly alarmed, he
shot the snake dead.

He claimed, that when measured,

it proved to be nearly 19
meters, over 60 feet long.

But Fawcett's account
was met with disbelief.

And he never provided convincing
proof, because soon after that,

he vanished into the Brazilian
jungle, and was never seen again.

The creature that
Fawcett encountered,

was almost certainly
a green anaconda.

Despite their massive
proportions,

these huge snakes
are seldom seen,

because they spend most
of their time in water,

waiting in ambush
for their prey.

In this murky world, they're
certainly well camouflaged,

and so, some people
believed, that somewhere

another real monster might
still be lurking, unseen.

In the 1960's a snake was
brought to the

Museum of Zoology, at
University College London.

This is it.

It had lived in London
Zoo for some years,

before it died, and
it was 5 meters long.

A lot of work went into
preparing the skeleton.

It had to be carried out,

onto the flat roof
of the museum,

and it was finally displayed,

in this rather unusual way.

Wrapped around the
branch of a tree.

For years the museum
displayed it as an anaconda.

But in 2012, a member of
the public saw

an old photo of the snake on
the museum’s website

and pointed out,
that it looked like

an African rock python,
and not an anaconda.

It’s unclear, how the
mistake came about.

The markings on the two
snakes, are quite different.

But both are giants.

And there’s much controversy,

as to which species, is
the largest snake of all.

Anacondas, pythons and
boas, like this one

don’t kill with venom.
They’re constrictors.

They squeeze their
prey to death.

And their coils can exert

a very strong pressure indeed,

as I can feel, with
this one on my arm.

But a big anaconda, can squeeze

with a force of
around 4,000 kilos.

That’s like having a
bus on your chest.

And that can certainly crush the
spine of a deer, or a capibara.

And yet, constrictor snakes,
don’t usually crush their prey.

In most cases, they simply
squeeze it so hard,

that the animal can’t breathe.

Every time it’s prey
tries to inhale,

the snake’s powerful
muscles squeeze harder.

The unfortunate victim
then, either dies because

it’s blood can no longer
circulate, or suffocates.

An anaconda, or a
python, can kill prey

that is not only twice
it's own body size,

but many times bigger
than it's head.

So, how does it manage to
swallow it’s victim whole?

Popular folklore has it,
that anacondas and pythons,

unhinge, or dislocate their
jaws to swallow large prey.

That is not true.

They do however, have
the ability to open

their mouths wider,
than most animals.

Pythons and anacondas,
have this additional bone,

attached to the
back of their jaws.

This provides a double
hinge, at the joint,

and allows them,
to open their jaws

extremely wide, both
downwards and sideways.

In addition, the two
sides of the lower jaw,

are not fused together, but
joined by an elastic ligament.

This gives the jaws
a lot of stretch,

and they can even move
apart, when the snake

is swallowing a large prey.

It also allows each
side of the jaw,

to move independently
of the other.

When eating a meal,
particularly,

one that is much
larger than itself,

the snake can alternatively

move it's jaws on either
side of it's head,

and walk it's prey
into it's mouth,

even while it's victim
is still alive.

As the jaws open wide,

the snake's elastic
skin stretches.

But the mobility of the
skull, comes with a price.

Many of the joints, that
in other snakes are solid,

have been replaced
by mobile ones.

So the skull has
less crushing power.

As a consequence, the
snake has to use

its entire body, to
overpower its prey.

Getting large prey into the
mouth, is one problem.

But how does a snake
push it all the way down

the length of its body,
into its stomach?

This is a Burmese python,

and it hasn't fed
for a long time.

So, I'm hoping to give
it a little breakfast,

with a dead rat.

Saliva from the salivary
glands in the mouth,

has moistened the prey,

so it's easier to swallow.

And now, it's moving its jaws,

drawing the rat farther
down it's throat

until eventually, the muscles
of the flanks take over,

squeezing the prey and
pushing against the ribs,

so that, it looks,
as though the snake

is as it were, crawling
around the rat.

And that will continue
for some time,

as the prey is worked down

into the snake's body,

until eventually, it
reaches the stomach,

which is around
the middle, here.

Equally remarkable is, what
happens inside the snake.

After months of
fasting, it has to

restart its digestive
system quickly.

Within a day, some of the
internal organs double in size.

The heart expands,

pumping greater volumes
of blood around the body.

And special cells in the
lining of the stomach,

produce powerful enzymes,

that break down flesh and bones.

And when the prey is
entirely digested,

the python's organs
return to normal again.

Anacondas and pythons
are able to take in

enormous meals, in
a single mouthful.

But how do they then survive
fasting for months on end?

Like all cold-blooded animals,

snakes get much of their
heat from the sun.

So they need less food
to fuel their bodies,

and most of what they eat,

is converted directly
into body mass.

Snakes continue to grow
throughout their lives,

and anacondas get bigger
than any other species,

because they live
mostly in water.

Their massive bodies,
supported by its buoyancy.

So, it's certainly
possible, that an anaconda

could grow, to an enormous size.

But how large can a
snake really get?

In 2009, further light was
shed on this question

with the discovery of the
fossils of a super snake.

It was given the
name "Titanoboa"

and it suggests that snakes
can get very large, indeed.

Titanoboa was nearly
13 meters long,

the length of a bus,

and must have
weighed over a ton.

It lived around 60
million years ago,

shortly after the extinction
of the dinosaurs.

We don't know for sure,
but it may be, that

the warmer climate of
the earth at the time,

allowed cold-blooded snakes,
to grow much larger in size.

What is certain, is that for
at least 10 million years,

Titanoboa was the largest
predator on the planet.

Both the camel and the anaconda

can withstand extreme
periods of fasting.

But it's only by looking
inside the camel's hump,

and the anaconda's stomach,

that we have
discovered the truth

behind their amazing

expandable bodies.

***