According to a friend of mine who has owned gerbils (I have never met one, as they are illegal in the state of California) says flame is unneccesary. Apparently gerbils have a fascination with holes - his tried to stuff itself into the barrel of his shotgun. It didn't matter if the hole was too small, the critter would just get back up and go at it again. Obsessed little creature.
I would be incredibly suprised if the purpose of gerbiling was stimulation due to death throes of the animal. I would expect any rodent in fear for its life would sink its teeth into the nearest hunk of flesh. Ever been bitten by a rodent? It's not something you would care to have done to your anus. Thus I find the stereotypical rationalization for gerbiling highly unbelievable.