Eerie voices. I was exploring a dungeon in Skyrim when a ghostly female voice suddenly rang out threatening me, that about made me fall out of my chair.

I'll certainly be doing creepy things with those tombs that pop open! It's too good to pass up. Though I don't know about having a companion with you. I think when you enter the place and start the horror part, you will be without anyone. And it will remain that way for most if not all of the mod. (Which will probably be like 1-2 hours long)

I remember a dungeon in FO3 that was pretty creepy... sounds with unseen sources. I think there was a door that opened by itself.

Something in this game scared the crap out of me but i cant remember what.. but err.. sudden things.. ussually a scary face pops up in-game and the dramatic shock music comes a second or 2 after or before the appearing of the face destroying the scariness of it all, make it SPOT-ON or it wont have the same effect..

FAT people! and they arent in Skyrim!

Hmm, I may have to get an animator to do a custom animation for 'slow creepy opening' instead of the normal door opening. Though the abrupt movement and noise may be enough to make it really scary...

Headcrabs.

I have to admit I have a slight holdover fear of the damn spriggans thanks to Bloodmoon. They're not nearly as bad in this game, but I still get that buttpucker moment every time. And trolls. The first time I ran into one in Oblivion, it cemented a never-ending relationship of fear, loathing and rage.

In all seriousness, though, ambient noises are great. The player adjusts to ambient noises over time, having established them as non-threatening, so random discordant noises punctuating the normal background noise is good. For another, speaking personally, I am actually less at-ease with no background music at all than if there were any playing. This is because I rely very heavily on the change in music to tell me if something out of my line of sight has aggro'd me. Also, random changes in lighting, particularly if it impairs the player's vision somewhat. It's hard to scare someone with a high sneak level, because they get to choose when the fight starts. Reduce that ability to predict what's out there, and it makes a huge difference.

Most definitely psycological horror. Like when walking through a dungeon you hear voices behind you, or you hear a strange clank echo from up ahead, or maybe a creepy baby crying in the distance, or while in a room you see a shadow move on the far wall.

bunnies and turkeys

things that jump out at you arn't scary, its shocking.
what really scares me are things i know is there, but don't know when or IF it will strike,
a giant fish in the water that i see coming, only to go past me to attack who knows when
a giant spider that appears, then climbs up into a hole on the roof of the cave i'm in would be pretty scary i think

Lags.