An hour underwater, without trying
How Does a Crocodile Hold Its Breath So Long?
A crocodile can lie on the bottom of a river for an hour. It is not holding its breath so much as switching most of itself off.
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Step 1 of 5
The heart slows right down.
As it submerges, a crocodile's heart drops to a handful of beats a minute. A slow heart uses far less oxygen, so the air already in its blood lasts far longer.
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Step 2 of 5
Blood goes only where it is needed.
Muscles and gut can wait; the brain and heart cannot. A crocodile can shunt blood away from everything that will survive the wait and keep the essential parts supplied.
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Step 3 of 5
It is cold-blooded, which helps enormously.
A warm body burns fuel constantly just to stay warm. A crocodile takes its temperature from the water, so it has no heating bill to pay while it waits.
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Step 4 of 5
Everything it needs is on top of the head.
Eyes, ears and nostrils sit in a line along the top of the skull, so a crocodile floats with the whole of itself hidden and only that strip showing.
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Step 5 of 5
A flap lets it open its mouth underwater.
A crocodile's throat is sealed by a flap of skin. It can grab something below the surface, mouth wide open, without any water going down into its lungs.
A crocodile's bite is one of the strongest measured, but the muscles that open its jaws are weak. A band round the snout will hold it shut.
The short version
A crocodile stays under for an hour by slowing its heart to a crawl, sending blood only to the brain and heart, and paying no heating bill.
Try it yourself
Sit very still and count your heartbeat, then run on the spot and count again. Slower means less oxygen used.