What scares you?

[Guest]

What is really scary, is that there are signs that there is SOMETHING out there, but you don't know where and what it is.

If I saw the thing, I might have an idea what to do. If its a ghost, you know that it can do little to you. If its a monster, you know that its a physical being. If its a mixture of the two though...

But it's worse when you don't know what it is. You do not know what to do, what it can do, you do not even know if its sentient.
Your antagonist can be a harmless rat, but it can still scare the shit out of you. The greater fear is that it is more then a rat.

It's even worse when you are alone, and in the dark. In the dark, you cannot see. You are blind and open to attack.

That can be very scary.