Humans do not have gizzards. Birds do have gizzards, because they do not have teeth. The gizzard’s function is to grind food in a bird's alimentary canal.
A gizzard is a part of a bird’s stomach. The gizzard’s walls are thick and made up of muscle. When a bird eats, the food goes through the esophagus and into the crop (a pouch-like structure).
From the crop, food enters the first part of the stomach, called the proventriculus, and the process of digestion begins. The gizzard contains grit, sand or small stones and is the second part of a bird’s stomach. These small stones pulverize food. Interestingly, all birds have gizzards, some insects and reptiles also have them.