Believe it or not...Seed eating birds, such as sparrows and finches, will eat mortar for the grit it contains. Birds have no teeth for crushing food items, so they utilise small, hard pieces of stone, or sand as abrasive digestive helpers. Birds swallow small bits of grit to act like teeth in the gizzard, a specialized stomach constructed of thick, muscular walls used for grinding up food. The grit helps to break down hard foods, such as seeds and the hard exoskeletons of some insects.