Sloths really are that strange, doing many things that other mammals do not.

The creatures move only sparingly, like crocodiles. They rarely defecate, like snakes. They can’t move their eyes without moving their heads, like owls. And their fur is often covered in algae, like, well, a rock. Or a turtle.

And now a new study published this month in the journal PeerJ finds that three-fingered sloths do another thing that’s highly unusual for a mammal—their metabolism shuts down when they get too hot or cold. This helps explain why the animals move so slowly: Sometimes, at extremes of temperature, they'd rather not move at all.

This is bizarre because when other large mammals experience extreme temperatures, they tend to use