Peristalsis facts for kids
The most familiar example of this is in the oesophagus. In the oesophagus, peristalsis pushes the ball of food down the oesophagus. The smooth muscle of the oesophagus contracts and relaxes in sequence, and this pushes the ball of food down the oesophagus.
The muscle is worked by a nervous mechanism called the "migrating motor complex". This works in one direction only, and also works in the lower regions of the digestive system.
Earthworms use a similar mechanism to drive their locomotion, and some modern machinery imitates this design.
Peristalsis Facts for Kids. Kiddle Encyclopedia.