What makes something scary

[GraphicsKid]

The most general answer I can come up with is this: things are scary when there's something unknown in a situation and the player's imagination is forced to come up with something.

For example: A long dark hallway is scary because we can't see what's down there, so we start thinking about what could be down there. Or what if there were a pair of glowing eyes at the end of the hallways? Now the player knows something is down there, but doesn't know what. It's probably not something pleasant!

I remember during my first few play-throughs, the monster sounds (not even the monsters, just the random sounds it'd play, like in the archives) were really scary because I hadn't yet seen what the monster looked like. I was forced to imagine something, and your imagination can always come up with something more frightening that what is put up on the screen.