The oesophagus is lined with muscle, and is lubricated. Its muscle pushes food down into the stomach. The oesophagus can contract or expand to allow for the passage of food. The muscular movement that pushes the food down the oesophagus is called peristalsis. At the entrance to the stomach there is a ring of muscle called a sphincter. This is usually closed, but relaxes as food approaches, allowing it to enter the stomach. In the stomach, the food is churned until it turns into a soupy mixture called chyme.