Here's why:
* Ruminants have a specialized four-chambered stomach that allows them to digest tough plant matter. They chew their food, swallow it, and then regurgitate it back to their mouth to chew again. Examples include cows, sheep, and goats.
* Non-ruminants have a simpler digestive system. They chew their food once and then digest it in a single stomach. Monkeys, like humans, are non-ruminants.
Monkeys eat a diet of fruits, leaves, and insects, which they digest in a single stomach.