Monsters, and Why They Aren't Scary.

[RedGroovy]

Changes in the enviroment, big and small, are scary as well. Not knowing what or whom could've been in there with you. For instance, you exit a room with all of the objects in their original positions, and as you re-enter examining, you notice an object(s) out of place. Little details like that play a big role in making you think and imagine things.

Silent Hill games were scary as hell (only in the beginning), due to the part that there wasn't any ambient music. It was total silence. So your ears were trained on focusing in on every little sound.

Amnesia would be perfect if it would get you to just generate an image or an idea of the monsters instead of you actually encountering any.

Also, mirrors scare the hell out of me.