Spiders, my biggest fear in video games since thief II : the metal age. Never after that i got so scared by a video game so much in an instant as to become numb... ah shame. But still, while big and noisy Skyrim spiders behave in a very predictable way (like any other mob...). What if they were faster, could jump on walls to flee from your sight, sneak on you in dark dark corners and move in that predatory way of theirs, catch you in their web and definitely descent from their hole in a different way. The first time i saw a frost spider get out of it's hole was very disappointing. Or maybe have some "trap" spider egg that when opened, a pack of tiny spiders crawling on you, would eat your face to death. That last one shouldn't be hard, just an animation sprite in first person would be enough. And then some miniaturized stock spiders walking on the body for the kill cam. Seeing as their is no much mods that alter the way creatures behave in their environment, i have few hopes but still a slightly scared man can dream. Kinda like that spider in Lord of the ring :
. For those wondering why i cried like a lil sissy from thief spiders, well it's thief, the only game where i can immerse myself completely. You could hear them, but you would not know where they come from, until you saw it. Then if by accident you opened their den, and started to whack them with your stick of a weapon in panic, they would randomly disappear from you sight buy jumping. Still making that hissing noise, to reaper somewhere behind you.