.It Wasn't Me.

His head did no thinking
His arms didn't move except when the wind cut up
Rough and mice ran around on the ground
He stood in a field where barley grows.

The black and green scarecrow is sadder than me
But now he's resigned to his fate
'Cause life's not unkind - he doesn't mind.
He stood in a field where barley grows.

Pink Floyd


Where does fart gas come from?
The gas in our intestines comes from several sources: air we swallow, gas seeping into our intestines from our blood, gas produced by chemical reactions in our guts, and gas produced by bacteria living in our guts.

What is fart gas made of?
The composition of fart gas is highly variable.
Most of the air we swallow, especially the oxygen component, is absorbed by the body before the gas gets into the intestines. By the time the air reaches the large intestine, most of what is left is nitrogen. Chemical reactions between stomach acid and intestinal fluids may produce carbon dioxide, which is also a component of air and a product of bacterial action. Bacteria also produce hydrogen and methane.
But the relative proportions of these gases that emerge from our anal opening depend on several factors: what we ate, how much air we swallowed, what kinds of bacteria we have in our intestines, and how long we hold in the fart.
The longer a fart is held in, the larger the proportion of inert nitrogen it contains, because the other gases tend to be absorbed into the bloodstream through the walls of the intestine.
A nervous person who swallows a lot of air and who moves stuff through his digestive system rapidly may have a lot of oxygen in his farts, because his body didn't have time to absorb the oxygen.
According to Dr. James L. A. Roth, the author of Gastrointestinal Gas (Ch. 17 in Gastroenterology, v. 4, 1976) most people (2/3 of adults) pass farts that contain no methane. If both parents are methane producers, their children have a 95% chance of being producers as well. The reason for this is apparently unknown. Some researchers suspect a genetic influence, whereas others think the ability is due to environmental factors. However, all methane in any farts comes from bacterial action and not from human cells.

What makes farts stink?
The odor of farts comes from small amounts of hydrogen sulfide gas and mercaptans in the mixture. These compounds contain sulfur. Nitrogen-rich compounds such as skatole and indole also add to the stench of farts. The more sulfur-rich your diet, the more sulfides and mercaptans will be produced by the bacteria in your guts, and the more your farts will stink. Foods such as cauliflower, eggs and meat are notorious for producing smelly farts, whereas beans produce large amounts of not particularly stinky farts.

Why do farts make noise?
The sounds are produced by vibrations of the anal opening. Sounds depend on the velocity of expulsion of the gas and the tightness of the sphincter muscles of the anus. Contrary to a popular misconception, fart noise is not generated by the flapping of the butt cheeks.

Why are stinky farts generally warmer and quieter than regular farts?
Most fart gas comes from swallowed air and consists largely of nitrogen and carbon dioxide, the oxygen having been absorbed by the time it reaches the anal opening. These gases are odorless, although they often pick up other (and more odiferous) components on the way through the bowel. They emerge from the anus in fairly large bubbles at body temperature. A person can often achieve a good sound with these voluminous farts, but they are commonly (but not always!) mundane with respect to odor, and don't feel particularly warm.
Another major source of fart gas is bacterial action. Bacterial fermentation and digestion processes produce heat as a byproduct as well as various pungent gases. The resulting bubbles of gas tend to be small, hot, and concentrated with stinky bacterial metabolic products. These emerge as the notorious, warm, SBD (Silent-But-Deadly), often in amounts too small to produce a good sound, but excelling in stench.
How much gas does a normal person pass per day?
On average, a person produces about half a liter of fart gas per day, distributed over an average of about fourteen daily farts.
Whereas it may be difficult for you to determine your daily flatus volume, you can certainly keep track of your daily numerical fart count. You might try this as a science fair project: Keep a journal of everything you eat and a count of your farts. You might make a note of the potency of their odor as well. See if you can discover a relationship between what you eat, how much you fart, and how much they smell.

How does a fart travel to the anus?
One may wonder why fart gas travels downward toward the anus when gas has a lower density than liquids and solids, and should therefore travel upwards.
The intestine squeezes its contents toward the anus in a series of contractions, a process called peristalsis. The process is stimulated by eating, which is why we often need to poop and fart right after a meal. Peristalsis creates a zone of high pressure, forcing all intestinal contents, gas included, to move towards a region of lower pressure, which is toward the anus. Gas is more mobile than other components, and small bubbles coalesce to from larger bubbles en route to the exit. When peristalsis is not active, gas bubbles may begin to percolate upwards again, but they won't get very far due to the complicated and convoluted shape of the intestine. Furthermore, the anus is neither up nor down when a person is lying down.

How long does it take fart gas to travel to someone else's nose?
Fart travel time depends on atmospheric conditions such as humidity, temperature and wind speed and direction, the molecular weight of the fart particles, and the distance between the fart transmitter and the fart receiver. Farts also disperse (spread out) as they leave the source, and their potency diminishes with dilution. Generally, if the fart is not detected within a few seconds, it will be too dilute for perception and will be lost into the atmosphere forever.
Exceptional conditions exist when the fart is released into a small enclosed area such as an elevator, a small room, or a car. These conditions limit the amount of dilution possible, and the fart may remain in a smellable concentration for a long period of time, until it condenses on the walls.

Why is there a 13 to 20 second delay between farting and the time it starts to smell?
Actually, the fart stinks immediately upon emergence, but it takes several seconds for the odor to travel to the farter's nostrils. If farts could travel at the speed of sound, we would smell them almost instantly, at the same time we hear them.

Is it true that some people never fart?
No, not if they're alive. People even fart shortly after death.