The first one is the whole 'oh em gee, that corpse isn't really a corpse' thing. Now I know that it's a bit of a horror game cliche, but I feel that bioshock did it really well. This is because it's not introduced as a game play element until about half way though the game, and because up until that point, every random corpse you saw had something that was lootable (money, bullets, food, etc) in it's pockets, so by that point in the game you have a urge to run right over to every corpse you see in a serach for free stuff. But then suddenly the corpses aren't just a place to get free stuff, they have the distinct possobility to not, infact, be a corpse, but a raving lunatic that's just waiting to jump up and try to eat/whack/shoot your face off.
The second one isn't really a game play element as it is a specific room that scared the crap out of me when I first played it. I'm taking about the secret button in Sinclair's Spirits and the whole area (well, 2 rooms) unlocked by it. For those of you who either haven't played the game, never got to that part, or just don't remember, here's a rundown of what happens: at that point in the game, you're in an area controlled by a mad artist who enjoys making plaster sculptures of people (in this case, the various enemies in the game) and putting them in dramatic/lively poses in various places. These things are EVERYWHERE in the area, and they are, in fact made of plaster and are totally harmless. You learn to accept them as part of the scenery pretty quickly. Anyway, later in the area, you enter a liqueur store called Sinclair's Spirits. In this store, there are six or so of those paster people statues just inside the entrace, all of them kind of making a tunnel with their arms. Farther inside, you find a button that unlocks a secret room (by the way, this whole thing in the shop with the button is a sidequest that you do to (I think) get to a weapon upgrade station). Inside the room that the button unlocks, there is a plaster dude sitting in a chair and a safe that you open to get a key or press another button (I cant remember which) that unlocks another room that's right outside the shop. Anyway, when you turn around after using the safe, the plaster dude in the chair is gone, but not in such a way that you really notice, but that your subconscious makes a note of it, in a 'hey, isn't this room a little different?' kind of way. Just enough to make you nervous. Then, when you get out you notice that all the plaster people in the entrance are gone. When I played this part for the first time, I had a wtf moment, where I did a double take, and was all like, 'wasn't there some stuff here before?' but then I just assumed that the six plaster people were in a different shop altogether, and that it was just my mind playing tricks on me. Anyway, you go into the second room, which is empty except for the upgrade station. Now, this room is rather large, and entirely empty, and when I say empty I mean EMPTY, as in not even some random litter on the floor or shelves on the wall, not even a air vent or something, just a upgrade station that's in the far corner. At this point, I was felling pretty freaked out, what with the seven missing plaster people from the liqueur store and all, so I'm being really cautious. So I go in, and carefully walk to the other end of the room to use the upgrade station, constantly checking my back to see if I'm being followed or if there's going to be a sudden flood of enemies coming behind me. So I'm walking across the room, looking around like a nervous rabbit, when BOOM, there's one of the plaster people behind me. I wasted almost a whole clip of tommy gun ammo on it as soon as I saw it, it startled me so much. So now I'm thinking, 'oh i c wat u did there game, er, I think' and turn around to continue, walk a few feet, and turn around again, and the plaster person is gone. More wtfs on my part, and I turn around again, and there it is, right in front of me in mid I-want-to-stab-you-in-the-face pose, and another clip of tommy gun is wasted due to startledness. Anyway, I continued across the room, and used the upgrade station, and when I was done, I turned around and all of the missing plaster people are in the room with me. Now, at this point I am freaking out, so I give all the plaster people a bullet or two for good measure, and start to walk back across the room to the exit, at which point EVERY SINGLE ONE COMES TO LIFE AND TRIES TO KILL ME. Because they weren't sculptures, they were enemies that were covered in plaster. I nearly shit myself.
Now that I think about it, this whole sequence is basically the 'Blink' episode of Doctor Who, you know, the one with the stone angels.
