Most people, even most kids, know that birds have no teeth. Likewise, it's common knowledge that quite a few birds consume hard foods such as grains and seeds almost exclusively. So what helps birds digest these tough morsels?
The answer lies in a bird's stomach -- in the lower part of its stomach, to be specific, the area called the gizzard. It's here that the powerful mixing and gnashing of food that occurs in human mouths takes place. But rather than bicuspids, molars, and the like, the gizzard uses small rocks, shells, and sand to break apart hard foods. The bird swallows these rocks and whatnot specifically to help with digestion. And when they wear down, as inevitably happens, the bird simply passes them on as waste and consumes a fresh supply. It's like having a drawer filled with spare teeth.
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