"It may leave a bitter taste, but peeing out their mouths produces more concentrated urea – and they can simply rinse and gargle away – lovely"

Should their marshy habitat dry up, Chinese soft-shelled turtles Pelodiscus sinensis do pretty well on dry land - as long as they can find puddles in which to dunk their heads.

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Biologists were long puzzled by this peculiar habit until 2012, when it was discovered that the turtles are not drinking, but peeing. Instead of excreting urea - the main waste product in urine - via their kidneys in the traditional manner, the reptiles expel it through the mouth lining.

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This unconventional toilet habit is thought to a key adaptation that enables the turtles to live in both fresh- and saltwater marshes.

Passing urea by the customary route would require them to drink large volumes of water to wash it through the kidneys - and in brackish marshes that could mean ingesting dangerously large quantities of salt.

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It may leave a bitter taste in the mouth, but this technique enables the turtles to produce urea in a more concentrated form and simply wash it out with a rinse and a gargle. Lovely...

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