A bird swallows its food whole without any ill effects. It can do this because it has a gizzard, an organ that is used as teeth and that is really part of the bird's stomach. The main function of the gizzard is to break up the food into small pieces so that it can be digested. The bird sometimes swallows small stones that also assist in grinding. With its gizzard, a bird can grind up even hard food,such as grain and other seeds.