It will be dusk or already dark as you enter through the gates at Screams Halloween Theme Park in Waxahachie, flames shooting skyward from the parapet of the haunted castle, fog rolling down the hill. You’ll walk past a cemetery, where mysterious dark figures lumber in the shadows. Immersed in Halloween for the evening—not just the 15 minutes or so that a standard haunted house might offer—you’re in for a frightful night. Lurking within are dozens of costumed actors, trained in the art of surprising their targets. After all, gory prosthetic wounds and menacing chainsaw props can only go so far: Getting scared is all about being startled.