supine. it is thought that large volumes of intestinal gas present low resistance, and can be propelled by subtle changes in gut tone, capacitance and proximal contraction and distal relaxation. this process is thought not to affect solid and liquid intra-lumenal contents. researchers investigating the role of sensory nerve endings in the anal canal did not find them to be essential for retaining fluids in the anus, and instead speculate that their role may be to distinguish between flatus and faeces, thereby helping detect a need to defecate or to signal the end of defecation. the sound varies depending on the tightness of the sphincter muscle and velocity of the gas being propelled, as well as other factors, such as water and body fat. the auditory pitch (sound) of the flatulence outburst can also be affected by the anal embouchure. among humans, flatulence occasionally happens accidentally, such as incidentally to coughing or sneezing or during orgasm; on other occasions, flatulence can be voluntarily elicited by tensing the rectum or "bearing down" on stomach or bowel muscles and subsequently relaxing the anal sphincter, resulting in the expulsion of flatus. management since problems involving intestinal gas present as different (but sometimes combined) complaints, the management is cause-related. pain and bloating main articles: abdominal distension and bloating while not affecting the production of the gases themselves, surfactants (agents that lower surface tension) can reduce the disagreeable sensations associated with flatulence, by aiding the dissolution of the gases into liquid and solid faecal matter. preparations containing simethicone reportedly operate by promoting the coalescence of smaller bubbles into larger ones more easily passed from the body, either by burping or flatulence. such preparations do not decrease the total amount of gas generated in or passed from the colon, but make the bubbles larger and thereby allowing them to be passed more easily. other drugs including prokinetics, lubiprostone, antibiotics and probiotics are also used to treat bloating in patients with functional bowel disorders such as irritable bowel syndrome, and there is some evidence that these measures may reduce symptoms. a flexible tube, inserted into the rectum, can be used to collect intestinal gas in a flatus bag. this method is occasionally needed in a hospital setting, when the patient is unable to pass gas normally. volume main articles: antiflatulent and carminative one method of reducing the volume of flatus produced is dietary modification, reducing the amount of fermentable carbohydrates. this is the theory behind diets such as the low-fodmap diet (a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, alcohols, and polyols). most starches, including potatoes, corn, noodles, and wheat, produce gas as they are broken down in the large intestine. intestinal gas can be reduced by fermenting the beans, and making them less gas-inducing, or by cooking them in the liquor from a previous batch. for example, the fermented bean product miso is less likely to produce as much intestinal gas. some legumes also stand up to prolonged cooking, which can help break down the oligosaccharides into simple sugars. fermentative lactic acid bacteria such as lactobacillus casei and lactobacillus plantarum reduce flatulence in the human intestinal tract. probiotics (live yogurt, kefir, etc.) are reputed to reduce flatulence when used to restore balance to the normal intestinal flora. live (bioactive) yogurt contains, among other lactic bacteria, lactobacillus acidophilus, which may be useful in reducing flatulence. l. acidophilus may make the intestinal environment more acidic, supporting a natural balance of the fermentative processes. l. acidophilus is available in supplements. prebiotics, which generally are non-digestible oligosaccharides, such as fructooligosaccharide, generally increase flatulence in a similar way as described for lactose intolerance. digestive enzyme supplements may significantly reduce the amount of flatulence caused by some components of foods not being digested by the body and thereby promoting the action of microbes in the small and large intestines. it has been suggested that alpha-galactosidase enzymes, which can digest certain complex sugars, are effective in reducing the volume and frequency of flatus. the enzymes alpha-galactosidase, lactase, amylase, lipase, protease, cellulase, glucoamylase, invertase, malt diastase, pectinase, and bromelain are available, either individually or in combination blends, in commercial products. the antibiotic rifaximin, often used to treat diarrhea caused by the microorganism e. coli, may reduce both the production of intestinal gas and the frequency of flatus events. odor bismuth the odor created by flatulence is commonly treated with bismuth subgallate, available over-the-counter in the us as devrom. bismuth subgallate is commonly used by individuals who have had ostomy surgery, bariatric surgery, faecal incontinence and irritable bowel syndrome. bismuth subsalicylate is a compound that binds hydrogen sulfide, and one study reported a dose of 524 mg four times a day for 3–7 days bismuth subsalicylate yielded a >95% reduction in faecal hydrogen sulfide release in both humans and rats. another bismuth compound, bismuth subnitrate was also shown to bind to hydrogen sulfide. another study showed that bismuth acted synergistically with various antibiotics to inhibit sulfate-reducing gut bacteria and sulfide production. some authors proposed a theory that hydrogen sulfide was involved in the development of ulcerative colitis and that bismuth might be helpful in the management of this condition. however, bismuth administration in rats did not prevent them from developing ulcerative colitis despite reduced hydrogen sulfide production. also, evidence suggests that colonic hydrogen sulfide is largely present in bound forms, probably sulfides of iron and other metals. rarely, serious bismuth toxicity may occur with higher doses. activated charcoal despite being an ancient treatment for various digestive complaints, activated charcoal did not produce reduction in both the total flatus volume nor the release of sulfur-containing gasses, and there was no reduction in abdominal symptoms (after 0.52 g activated charcoal four times a day for one week). the authors suggested that saturation of charcoal binding sites during its passage through the gut was the reason for this. a further study concluded that activated charcoal (4 g) does not influence gas formation in vitro or in vivo. other authors reported that activated charcoal was effective. a study in 8 dogs concluded activated charcoal (unknown oral dose) reduced hydrogen sulfide levels by 71%. in combination with yucca schidigera, and zinc acetate, this was increased to an 86% reduction in hydrogen sulfide, although flatus volume and number was unchanged. an early study reported activated charcoal (unknown oral dose) prevented a large increase in the number of flatus events and increased breath hydrogen concentrations that normally occur following a gas-producing meal. garments and external devices in 1998, chester "buck" weimer of pueblo, colorado, received a patent for the first undergarment that contained a replaceable charcoal filter. the undergarments are air-tight and provide a pocketed escape hole in which a charcoal filter can be inserted. in 2001 weimer received the ig nobel prize for biology for his invention. a similar product was released in 2002, but rather than an entire undergarment, consumers are able to purchase an insert similar to a pantiliner that contains activated charcoal. the inventors, myra and brian conant of mililani, hawaii, still claim on their website to have discovered the undergarment product in 2002 (four years after chester weimer filed for a patent for his product), but state that their tests "concluded" that they should release an insert instead. incontinence main article: faecal incontinence flatus incontinence where there is involuntary passage of gas, is a type of faecal incontinence, and is managed similarly. society and culture he-gassen (detail), an art scroll depicting a battle of flatulence, from japan during the edo period in many cultures, flatulence in public is regarded as embarrassing, but, depending on context, may also be considered humorous. people will often strain to hold in the passing of gas when in polite company, or position themselves to silence or conceal the passing of gas. in other cultures, it may be no more embarrassing than coughing. while the act of passing flatus in some cultures is generally considered to be an unfortunate occurrence in public settings, flatulence may, in casual circumstances and especially among children, be used as either a humorous supplement to a joke ("pull my finger"), or as a comic activity in and of itself. the social acceptability of flatulence-based humour in entertainment and the mass media varies over the course of time and between cultures. a sufficient number of entertainers have performed using their flatus to lead to the coining of the term flatulist. the whoopee cushion is a joking device invented in the early 20th century for simulating a fart. in 2008, a farting application for the iphone earned nearly $10,000 in one day. a farting game named touch wood was documented by john gregory bourke in the 1890s. it existed under the name of safety in the 20th century in the u.s., and has been found being played in 2011. in january 2011, the malawi minister of justice, george chaponda, said that air fouling legislation would make public "farting" illegal in his country. when reporting the story, the media satirised chaponda's statement with punning headlines. later, the minister withdrew his statement. environmental impact the flatulence of cows is only a small portion (around one-twentieth) of cows' methane release. cows also burp methane, due to the physiology of their digestive systems. flatulence is often blamed as a significant source of greenhouse gases, owing to the erroneous belief that the methane released by livestock is in the flatus. while livestock account for around 20% of global methane emissions, 90–95% of that is released by exhaling or burping. in cows, gas and burps are produced by methane-generating microbes called methanogens, that live inside the cow's digestive system. proposals for reducing methane production in cows include the feeding of supplements such as oregano and seaweed, and the genetic engineering of gut biome microbes to produce less methane. since new zealand produces large amounts of agricultural products, it is in the unique position of having high methane emissions from livestock compared to other greenhouse gas sources. the new zealand government is a signatory to the kyoto protocol and therefore attempts are being made to reduce greenhouse emissions. to achieve this, an agricultural emissions research levy was proposed, which promptly became known as a "fart tax" or "flatulence tax". it encountered opposition from farmers, farming lobby groups and opposition politicians. entertainment main article: flatulist historical comment on the ability to fart at will is observed as early as saint augustine's the city of god (5th century a.d.). augustine mentions men who "have such command of their bowels, that they can break wind continuously at will, so as to produce the effect of singing". intentional passing of gas and its use as entertainment for others appear to have been somewhat well known in pre-modern europe, according to mentions of it in medieval and later literature, including rabelais. le pétomane ("the fartomaniac") was a famous french performer in the 19th century who, as well as many professional farters before him, did flatulence impressions and held shows. the performer mr. methane carries on le pétomane's tradition today. also, a 2002 fiction film thunderpants revolves around a boy named patrick smash who has an ongoing flatulence problem from the time of his birth. since the 1970s, farting has increasingly been featured in film, especially comedies such as blazing saddles and scooby-doo. religion in islam, flatulence, if audible or odorous, invalidates wudu (ablution or ritual purity), if the person who passed gas suffers from ocd about passing wind. however, in normal cases, flatulence, even if inaudible and odorless, nullifies ritual ablution if the person is certain that he had passed gas. personal experiences people find other peoples' flatus unpleasant, but are unfazed by, and may even enjoy, the scent of their own. while there has been little research carried out upon the subject, some speculative guesses have been made as to why this might be so. for example, one explanation for this phenomenon is that people are very familiar with the scent of their own flatus, and that survival in nature may depend on the detection of and reaction to foreign scents.