Ghosts
I'm scared of ghosts. That's not to say that I necessarily believe in ghosts, but they scare me just the same. The thought of something that's real, but not QUITE that real, is frightening. A lot of my favourite works of horror fiction--that is to say, the ones that stick with me--either involve ghosts ( Poltergeist) or ghost-like entities (Sheridan Le Fanu's "The Green Tea"). I think it's the psychological element--a creature that you can see but other's can't, or that manifests itself in ways that shouldn't be possible--isn't just an attack on the body, but on the mind. Probably the movie that scared me the most was the 2015 documentary The Nightmare, which is about sleep paralysis and the visions that may accompany it. I know what sleep paralysis is, and I know that the images that accompany it are just that--images. The shadowmen are not real and cannot hurt me--and yet I bought and started wearing a sleep mask right after watching it...