Flatulence consists of gases that are built up in the gastrointestinal tract of mammals and are released through the anus.
The gases are most often produced by swallowing air, and frequently produced by certain types of food, mostly the fibrous or starchy type and the person's digestive system's reaction to them. The list includes beans, yams, sweet potatoes, chickpeas, citrus rinds, chestnuts, broccoli, cabbage, yeast in breads, etc. In beans, the most notorious offenders in this regard, the problem seems to arise from starch molecules resistant to digestion: when the polysaccharides reach the intestines, gut bacteria feed on them, producing gas. In the case of those with lactose intolerance (ie. most non-Caucasian humans), gut bacteria feeding on lactose can give rise to excessive gas production. Another source of excessive gas production in the stomach is stress. Stressful situations can cause the stomach to produce gas. Also, not only does tight clothing cause a gassy stomach to be painful, it also can contribute to the production of gas.
Many people notice if they reduce their intake of most refined carbohydrates such as rice, pasta, potatoes, and breads, their stomach gas production decreases significantly.
Breastfeeding mothers are advised to avoid gas producing food in their diet because breastfed babies can vomit when there is too much gas in their stomach.
Methane is the primary gas released; bovine flatulence is one of the primary sources of this greenhouse gas. As methane is flammable, some flatulence is as well. The gas released often has a foul odor which mainly results from sulfur compounds such as hydrogen sulfide that are the result of protein breakdown.
In many human cultures, excessive flatulence is regarded as embarrassing and impolite, even to the point of being a taboo subject; and hence a natural subject for toilet humour: see Blazing Saddles, Le Pétomane,Kangaroo Jack, and Austin Powers, among others. Flatulence can be considered funny to some people.
A lot of the humour focuses on either the smell of the gas (thus, the "silent but deadly" flatulence), or the wide variety of noises that passing flatulence produces.