Provoking and Maintaining Horror

I've seen a lot of things about how horror is hard to create and maintain, especially in certain settings.  And that's true.  However, most of the advice about running horror doesn't focus on those challenges.  It caters to horror's strengths.  That's not bad, but it misses out on some opportunities.

Even if you don't play horror games, most gamers have experienced horror.  It might be very slight — sure, everyone is laughing and rattling dice in a well-lit room, but there is a sinking feeling of dread when it looks like everything is about to go badly.  From the Game Master's perspective, you see it when things start accelerating.  Suddenly, the players are talking at once, as if screaming actions the loudest will somehow save them.

Chances are good that this wasn't a horror game.

A couple of weeks ago, I was running Seekers of the Ashen Crown when the players came upon a trap.  They're pretty well prepared for this dungeon, but they didn't necessarily know that.  All they knew was that the trap would attack every round until it reset, and they didn't know how long that would be.  While the party escaped more depleted than when they entered, they left the trap alive and without any long-term dismemberment.

That's a big part of horror gaming: as the GM, you know what's happening.  The players don't.  Even if they are experienced with the setting at hand, they don't have to feel comfortable.  Rely on description rather than identification.  Maybe the characters have seen (and defeated) eighty goblins, but in a darkened, shadowy hallway, it's "a small, loping shape, half-hidden in the shadows on the walls.  You think it's humanoid, but it's hard to tell.  What do you do?"

Another important technique is to use the characters' strengths against them.  This isn't something I would recommend all the time — players tend to get annoyed when they can't play the character they signed up to play — but it's sometimes effective to show characters in a fantasy or science fiction setting that their abilities may not be enough to save them.  This is particularly effective if their abilities are useful, but not as useful as they would normally be.  Maybe a race of beetle-things has taken up residence on their ship; the beetle-things' armor isn't impervious to their bullets, but they can take enough hits that one beetle-thing could probably take out one fully-armed space marine.  This forces everyone to conserve resources and plan the attack a little more carefully.

Basically, if the outcome is in doubt, but everyone feels reasonably confident, it's action.  If the characters and/or players aren't confident, it's horror.  Use that to your advantage.