Lacking teeth, they swallow pebbles that act as gastroliths to grind food in the gizzard. An earthworm's digestive system consists of a mouth, pharynx, esophagus, crop, gizzard, and intestine. Their stomachs also often contain gizzard stones. All species have a radula and gizzard plates. In Indonesia, gizzard and liver are considered part of a complete fried poultry dish. In Northern China, one can find barbecued duck gizzard. Once through the gizzard, food continues through the intestine for digestion. The mouth opens into a sclerotised oesophagus, which leads to a crop and gizzard. Grit aids in digestion by grinding food as it passes through the gizzard. Several roundworm and spirurid species have been found in the lining of the gizzard. In Korea, chicken gizzard, called "dak-ttongjip", is stir-fried and eaten as anju or yasik. Chickens' heart, gizzard ("gi-la") and liver are also enjoyed. The prey is mostly swallowed whole and is ground up by stones in the gizzard. Several contemporary sources state that the dodo used Gastroliths (gizzard stones) to aid digestion. Both birds and dinosaurs use gizzard stones.