Horror movies have the extra perk of being able to use music to create the mood and to shape how the audience views things.

Scary music tells us to be scared, it gears up that tension. Having music and then suddenly cutting it off, leaving the viewer waiting for something to happen.

Writers don't get that. We have to use words and pacing to gear things up, to lure the reader in. If we drag things on too much, we lose that tension. If everything's always tense, then the reader never gets a surprise jolt.

Humor or having the characters relax for a bit can allow the writer to throw in a scene to leave the reader's head spinning.