A series of normal coordinated, rhythmic muscle contractions that occurs automatically to move food through the digestive tract, urine from the kidneys through the ureters into the bladder, and bile from the gallbladder into the duodenum . Peristalsis is a normal function of the body to move fluid from one place to another. It can sometimes be felt in the abdomen as gas is moved along. Peristaltic waves look much like the muscle contractions of a snake's underbelly that enable it to move along a surface.