I found this urban legend pretty funny. Snopes confirms that it’s completely false. This legend was started in 1993
"In retrospect, lighting the match was my big mistake. But I was only trying to retrieve the gerbil," Eric Tomaszewski told bemused doctors in the Severe Burns Unit of Salt Lake City Hospital. Tomaszewski, and his homosexual partner Andrew "Kiki" Farnum, had been admitted for emergency treatment after a felching session had gone seriously wrong. "I pushed a cardboard tube up his rectum and slipped Raggot, our gerbil, in," he explained. "As usual, Kiki shouted out "Armageddon", my cue that he'd had enough. I tried to retrieve Raggot but he wouldn't come out again, so I peered into the tube and struck a match, thinking the light might attract him." At a hushed press conference, a hospital pokesman described what happened next. "The match ignited a pocket of intestinal gas and a flame shot out the tube, igniting Mr Tomaszewski's hair and severely burning his face. It also set fire to the gerbil's fur and whiskers which in turn ignited a larger pocket of gas further up the intestine, propelling the rodent out like a cannonball." Tomaszewski suffered second degree burns and a broken nose from the impact of the gerbil, while Farnum suffered first and second degree burns to his anus and lower intestinal tract.