What is a fart, exactly?
Farts are caused by trapped air, which can come from many sources. Some of it is air that we have swallowed while chewing or drinking. Some air is caused by gas seeping into our intestines from our blood, and some gas is produced by chemical reactions in our intestines or bacteria living in our guts. A typical fart is composed of about 59 percent nitrogen, 21 percent hydrogen, 9 percent carbon dioxide, 7 percent methane and 4 percent oxygen.
Only about one percent of a fart contains hydrogen sulfide gas and mercaptans, which contain sulfur, and the sulfur is what makes farts stink. Farts make a sound when they escape due to the vibrations of the rectum. The loudness may vary depending on how much pressure is behind the gas, as well as the tightness of the sphincter muscles.
