In 1941, the werewolf mythology gained an iconic set of lines in the Universal horror classic The Wolf Man: “Even a man who is pure at heart/and says his prayers by night/May become a wolf when the wolfsbane blooms/and the autumn moon is bright.” Forty years later, from the same studio, a less delicate line was added to the lycanthrope canon: “I will not be threatened by a walking meat loaf!” Such is the tone of An American Werewolf in London, one of the best horror-comedies of the past few decades. It’s…