Farts are flammable
As stated above, the methane and hydrogen in bacteria-produced farts make your gas highly flammable. This is why some people think it’s a fun party trick to hold a lighter up to their bums and let one fly; doing so produces a big burst of flame, but is obviously very dangerous. In rare cases, a build-up of flammable gasses in the intestines have caused explosions during intestinal surgeries!