The relationship between vulgar humor and repulsive horror is particularly close. It’s no accident that after helping pioneer the slasher movie with the 1974 sorority house thriller “Black Christmas,” the Canadian director Bob Clark went on to make “Porky’s,” the dirty godfather of the raunchy teenage sex comedy. While the past few decades have made these movies seem far less shocking than they once were, these commercial genres still trade on shock.

And the pacing is similar. Just look at audiences watching them. They start relaxed, then become increasingly tense as the action builds, and then after the big reveal, be it a joke or a kill, the viewers’ anxiety dissipates audibly with either a laugh or a gasp. At scary movies the first thing audiences typically do after screaming is laugh at themselves. While explicit material may turn off some, others become more alert.