Retroperistalsis

Retroperistalsis is the reverse of the involuntary smooth muscle contractions of peristalsis. It usually occurs as a precursor to vomiting.

Peristalsis moves food through the gastrointestinal tract from the esophagus in the direction of the anus.

Local irritation of the stomach, such as bacteria or food poisoning, activates the emetic center of the brain which in turn signals an imminent vomiting reflex, food moves in the opposite direction, often from the duodenum of the small intestine into the stomach.