Why so scary?: Possession
One of the first child horror heroines, Regan's possession by the Devil is still possibly the most explicit and gruesome depiction of what could happen if Satan ever took a fancy to you. Like it or not, religion is all around us and these fictional evil entities tap into this vast backdrop of spirituality.
Drawing on the horror we have at seeing children do terrible things, William Friedkin's 'The Exorcist' highlights the terrible side effects that possession could have, including frightening your mum, embarrassing social situations and, frankly, a lot of pain.