Some animals have an organ called the gizzard. The gizzard is muscular and helps to crush up hard food. Earthworms and many birds, including chickens, have gizzards. Chickens swallow small rocks that help the gizzard to grind up food. Did plant-eating dinosaurs have gizzards too? No one has found an actual dinosaur gizzard, but they have found small piles of round rocks inside dinosaurs’ ribcages.
Based on its function, the gizzard is part of the *blank*
system.