Mechanical digestion is the physical breakdown of food. The act of chewing is technically called mastication. Teeth are used to mechanically break down food into smaller, softer pieces. This increases the surface area and also warms up the food. Chemical digestion begins in the mouth, continues in the stomach, and finishes in the small intestine. Enzymes in the mouth saliva starts to chemically break down food, particularly carbohydrates. Chemical digestion continues in the stomach. Gastric juices in the stomach contain hydrochloric acid and pepsin and start breaking down proteins. Muscles in the stomach lining mix up the food with the gastric juices for a more effective breakdown.