The purpose of horror movies is to frighten you, but that doesn't mean cast and crew have to be anxious and terrified all the time. (Some directors disagree, but that's a different issue.) Behind the scenes, horror productions are more like Halloween parties where the treat is that you get to be in movies. (The trick is getting a good agent.) When the performers aren't trying to chill you, they just, well, chill -- in dress-up. And the show business counterpart of water cooler conversations shows movie monsters in a different light.
Source: Bloody Disgusting
Source: Screen Rant
Source: Dangerous Minds