Sloths eat leaves with very little nutritional value; in fact, it takes up to a month for their food to digest. To compensate, they have a metabolic rate about half that of other mammals their size. Since they can’t run away from predators or fight them off easily, they hide instead. Hanging below branches makes them less visible to harpy eagles and their claws can grip the branch without using any energy – indeed, sloths won’t fall from a tree even if they’re shot! Sloths spend so much time upside down that their fur lies the opposite way to most mammals, growing from the paws up to the body.
Answered by Luis Villazon.