Horror films are filled with jump scares, moments that shock and startle viewers as monsters, serial killers, ghosts and even cats pop out of the darkness. But while jump scares are a very common element to include in a scary movie, they don’t always work as intended, and often, you might just end up laughing instead of screaming. To find out what goes into creating an effective jump scare we spoke with Rebekah McKendry. a film professor at USC who specializes in horror. What makes certain scenes in “The Conjuring,” “Insidious,” and “The Exorcist 3” so terrifying while others like in “Friday the 13th Part VIII: Jason Takes Manhattan” fall flat?