Human flatulence contains combustible gases including methane and hydrogen produced by colonic bacterial fermentation, making the claim trivially true and common knowledge.
The retrieved papers focus on animal enteric methane, natural gas reservoirs, hydrogen sulfide immunity, and human breath tests, none of which directly evaluate the chemical composition or flammability of human flatulence. However, the claim is a matter of basic everyday observation and scientific fact (gastrointestinal gas contains methane and hydrogen, both of which are flammable), rendering it common knowledge requiring no citation.