If you were to look for a three-toed sloth in the wild, you might have difficulty finding one. They spend nearly all their time high in trees, clinging to limbs with their long toenails. Frequently, they are curled in an upside-down ball sleeping. When sloths do move, they look like a video in such slow motion that a predator may not even notice. A sloth's naturally brown fur blends in with tree bark, helping to camouflage it. Three-toed sloths have a greenish hue, thanks to algae that live in their fur in what is thought to be a mutualistic relationship (additional camouflage for the sloth and habitat for the algae). Only about once per week do three-toed sloths descend to the ground, where they dig a latrine, defecate, and cover up their waste. This excursion makes them vulnerable to predation by snakes or jaguars, and they lash out with their sharp claws if attacked.

Mammals have a unique arrangement of a lower jaw directly hinged to the skull. The upper jaw is fixed, while the lower jaw is movable. A powerful bite results which, coupled with specialized teeth, allows mammals to eat a diversity of foods. Straight-edged incisor teeth at the front of the jaw are for cutting and gnawing. Pointed, canine teeth on the sides can grab and tear meat. Flat, broad molars are used to grind or crush plants or shelled animals. Mammals tend to have more than one type of tooth (heterodont dentition), with the mix depending on diet. Meat-eaters have sharp incisors and canines plus slicing molars; mammals who eat tough plants have duller incisors and canines, but large, ridged molars. All types of mammal teeth are replaced once or never during a mammal's lifetime. A coating of enamel, the hardest material found in a mammal's body, makes teeth built to last.