Fart, Flatulence - Flatulence is the expulsion through the rectum of a mixture of gases that are byproducts of the digestion process of mammals and other animals. The mixture of gases is known as flatus, (informally) fart, or simply gas, and is expelled from the rectum in a process colloquially referred to as 'passing gas' or 'farting'. Flatus is brought to the rectum by the same peristaltic process which causes feces to descend from the large intestine. The noises commonly associated with flatulence are caused by the vibration of the anal sphincter, and occasionally by the closed buttocks.