Nothing.
I'm being serious here, but the thing that really fucking scares me, isn't when something "scary" is happening, it's when something isn't happening. I don't know how many nights I spent unable to go to sleep, because I'm scared that something's going to pop out of nowhere and start doing something I'd rather prefer it didn't the second I close my eyes. The worst bit is, I know that there's absolutely nothing anything could do that'd be worse than the sheer apprehension of just waiting for this to happen, even though I know it won't.
Oh, I worry about things, sure, I'm shocked by things, I might even be unnerved by some things, but I think, these days, this is the only thing that really scares me.