Mouth
. Mouth, opening in an animal's body used for taking in food. Mouths are also typically used for making sounds, such as barks, chirps, howls, and in humans, speech. In most animals, the mouth is found on the face, near the eyes and nose. Lips, which form the mouth's muscular opening, are an especially familiar part of the body for humans. Lips help hold food in the mouth and are used to form words during speech. They also help form facial expressions, such as smiling and frowning. Lips open wide during a yawn and squeeze together during a whistle. Lips are darker than the surrounding skin because of the many extremely small blood vessels, called capillaries , that show through the skin. The cheeks form the sides of the mouth. They are composed of muscle tissue that is covered on the outside by skin. Like the lips, the cheeks help hold food and they also play a role in speech. Inside the mouth is the large, muscular tongue . This extremely flexible muscle is used for eating and