Complex sentence: 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.
Split into simpler sentences: 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 then moves in the opposite direction, often from the duodenum of the small intestine into the stomach.