Sloths are weird critters. Cute, in a certain light, but mostly weird. They’re members—with armadillos and anteaters—in a superorder of mammals called the Xenarthra, which are united by a unique form of multi-jointed vertebrae. Their diet consists mostly of leaves, which are poor quality food, and hard to digest. Fortunately, they also have one of the slowest, lowest-energy lifestyles of any mammal, using heavily modified limbs to hang upside down from branches while they browse, their most recent meal fermenting in their guts.
David Attenborough got up close with a sloth—which he calls a “mobile compost heap”—in The Life of Mammals. He also observes one of the sloth’s weirdest behaviors: to answer the call of nature, it climbs all the way down to the ground.
Why do sloths go to all that trouble—and risk—just to poop? Well, according to a recent paper in Proceedings of the Royal Society, they do it to feed poop-eating moths that help cultivate nutritious algae in their fur. No, but really.