An American Werewolf in London is part of a very honourable cult genre: the werewolf/vampire film. The rules of these films are standardised. Vampires are blood-drinking, living corpses whose mere bite can make you one of their number. Werewolves are people who turn into wolves, or wolf-like humanoids, at every full moon, and their bite turns other humans into werewolves. Vampires can only be killed by fire, removal of the head or a stake through the heart. Werewolves can only be killed by a silver bullet or the SAS.