Three-toed sloth (Bradypus variegatus)
With hook-like claws, sloths hang around in the canopy dining exclusively on leaves. Most mammals couldn’t survive on a diet of low-protein—and sometimes toxic—leaves. But slow-moving sloths have a special digestive system helps them neutralize leaf toxins while an extremely slow metabolism and low body temperature conserve energy. Two-extra neck vertebrae help them swivel their heads nearly 270° without using energy to move their bodies.