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Fingernails sometimes fall off when they’re damaged — like if they get stuck in a car door.

That has to do with what’s known as the matrix, the spot at the bottom of your nail that’s responsible for growing your nail. Nails themselves are actually little plates of proteins called keratin. All of those proteins are connected, which is what makes one continuous nail.

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When your finger experiences a shock, like getting stuck in a car door, the matrix temporarily pauses the growth of the fingernail. That pause means the proteins are no longer connected. So the new part of the nail that starts growing isn’t connected to the old part that you could already see — which is why your fingernail falls off.

We investigate the strange science of fingernails in the latest episode of our video series “Boddities.”

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