RAGGED tooth shark babies munch on their own siblings from inside their mum's womb, a gruesome new animal documentary has revealed.

The shocking scenes in Richard Attenborough's Story of Life captures mother nature at its most brutal.

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Pregnant ragged tooth sharks – also known as sand tiger sharks – migrate to warmer waters to help their babies grow quicker.

But the warm water makes them sleepy, Richard Attenborough explains, causing them to forget to eat.

Their gigantic jaws and terrifying teeth begin to harbour nasty growths as they lose nutrition.

And so their unborn pups must fend for themselves.

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Two of the largest cubs will eat the rest of the pack to save themselves, the gruesome BBC clip reveals.

Attenborough explains: "Inside each female infant teeth are being put to good use, as the female's two largest unborn pups slowly eat their siblings".

Although it sounds gruesome, "it ensures only the strongest and largest babies survive," Attenborough adds.

The mum will travel south to cooler waters before going into labour.

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It's the only form of cannibalism seen in mammals.

But its not the first time animals have been seen eating each other.

In one instance of horrific animal abuse starving zoo animals began eating each other.

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