Birds Eat Grit - birds which peck grain and other seeds also peck grit to help them to digest these hard foods. Because birds have no teeth, the work of chewing, which would require muscles and strong jaw bones, is done by the gizzard. This makes it possible for the skull to be delicate in structure and therefore light in weight. Grit is taken into the 
gizzard, or ventriculus, which has thick and often very muscular walls and the combined action of the two grinds down the hard food. The ventriculus is the back part of a bird's stomach, the fore part is glandular and secretes digestive juices and is called the proventriculus. Food passes from the ventriculus to be absorbed by the intestines.