Three-Toed Sloth

The pale-throated three-toed sloth hangs upside down from a single hook-like claw grip for hours, moving so slowly that green algae grow in its fur and give it camouflage among the leaves it eats. Everything about it is budgeted around a leaf diet — the slowest-digesting food a mammal can eat.

Once a week or so it descends to the forest floor, its most dangerous moment, to relieve itself at the base of a tree. On the ground it can barely walk, dragging itself along on its elbows.