The digestive system of a dog is very different from that of a human. Dogs and cats have four stomachs and three sets of intestines, which help break down food and water. Dogs do not eat solids, only liquids. However, a dog's digestive tract is designed to quickly break down food and move it through the system. This is why dogs have no teeth in their stomach. They don't need to chew their food and don't need to spend time chewing before swallowing. It takes about 20 minutes for a dog's stomach to empty.