The rumbling people hear in their stomachs is formally called Borborygmus. Taken from Wikipedia:
"The "rumble" or "growl" sometimes heard from the stomach is a normal part of digestion. It originates in the stomach or upper part of the small intestine as muscles contract to move food and digestive juices down the gastrointestinal tract and functions as a sort of intestinal "housecleaning"."
Hope this helps!
Vicki M
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