The Chinese soft-shelled turtle looks like someone glued the snout of a pig onto the face of a fish, with the texture of a scrotum for good measure. But its bizarre appearance pales in comparison to an even more bizarre, and newly discovered, habit: it expels waste through its mouth.
When the turtle breaks down proteins in its liver, it ends up with an abundance of nitrogen, which it expels from its body in the form of urea. Humans are the same—we get rid of urea in the form of urine, via our kidneys. But the soft-shelled turtle has an altogether different route.
It’s well-adapted to life in the water, and lives in salty swamps and marshes. But Yuen Ip from the National University of Singapore noticed that when the turtle emerges from water, or is stranded on land during dry spells, it will plunge its head into puddles. While submerged, it rhythmically expands and contracts its mouth. Ip found that the turtle gets rid of most of its urea through its mouth rather than its kidneys, via gill-like studs in its mouth. It can breathe and get rid of waste through the same structures.
[Update: Note the comments below. Urine is more than just dissolved urea, so while the stuff the turtle spits out is similar, it's not quite the full deal.]