Making a Horror Game Scary

GameSetWatch has put up an article about the characteristics that give games in the survival-horror genre the ability to unnerve, startle, and scare players in ways that most games don't. The genre has seen a resurgence lately, with titles like Dead Space, F.E.A.R. 2, and Left 4 Dead posting strong sales numbers. What triggers your fight-or-flight impulses in games like these? From the article:
"Being visual creatures, humans are most comforted by sight because of our ability to discern objects, action and consequences based on a picture. As a result, cutting visual stimuli and sticking purely to audio or speech is one of the best ways to keep a player on their toes. Even with weapons, it's very hard to find what you cannot see, and what you do not know. Even if visual stimuli is used, limiting or obfuscating the player's view can enhance the horror in a game, especially if the player sees it for an incredible short time. This can hint both at the difficulty of an upcoming encounter, or even allude to matters earlier in the narrative that the player will soon have to face."

http://games.slashdot.org/games/09/03/01/0639247.shtml