Farts consist largely of inflammable methane gas. Lighting such gas can result in burns or explosions. Clothing may catch fire or sensitive tissues can be damaged.
Such experiments are common among young men on camping trips or in single-sex group residences such as dormitories or fraternity houses, but the inflammability of bodily gases has caused serious problems in the operating room and also in slaughterhouses.
At least one patient is known to have exploded while undergoing cauterization of a rectal polyp. An electric spark ignited the patient's intestinal gases, resulting in a six-inch (15-cm) hole in their large intestine. However, this was sewn up, and the patient recovered [1].
In the film South Park: Bigger, Longer and Uncut, the character Kenny McCormick kills himself attempting to light one of his farts. (Kenny's deaths from odd causes are a running gag in the series.)