They are characterized by a large stomach which is divided into two chambers. The leaves sit for long hours in the upper chamber which is kept acid free. Some people think that their striking black and white fur makes these animals the most beautiful of all primates. Because they live in fairly large groups, it is also suspected that, when they flee predators, the blur of numerous black and white patches of fur can serve to confuse the pursuer.
Similar logic is applied in explaining the black and white stripes on zebras.