In Vacancy, editing creates a false sense of space, which effectively misleads and unnerves audiences.
A killer is chasing David and Amy, a married couple, in an underground tunnel. Because the tunnel is tight, we can't see who is where in relation to each other. We know that David is ahead of Amy, and the killer somewhere behind, but that is all. We don't know how far behind the killer is, or if he can see them.
We see only brief, repetitive shots of David, Amy, and the killer, sometimes from the front, sometimes from behind. Edits are quick, creating a sense of panic. Our inability to know how close the killer is, or whether any of the shots are his POV (point of view), unnerves us. Dim lighting further contributes to the audience's confusion.
David (Luke Wilson) finally reaches the exit. Amy (Kate Beckinsale) turns and looks behind her.
We cut to this shot of the killer emerging from a tunnel, and turning right. He appears to be looking at Amy!
This is because this edit creates two eyeline matches. Amy's eyeline in the previous shot appears to be directed at the killer in this shot. And the killer's eyeline in this shot appears to be directed at Amy in the previous shot. One eyeline match would have been enough to create a sense that the two shots share the same space.
Two eyeline matches double this sense of shared space. This sense of shared space is further supported by the 180 degree line that is created by this edit. Amy looks leftward, and the killer looks rightward. This places the two characters on the same side of an imaginary 180 degree line, creating the sense that we know where each is in relation to the other. Amy is to the killer's right. The killer is to Amy's left.
However, we then cut to the killers POV -- and see an empty tunnel!
Vacancy's editing has fooled the audience! The killer was not behind David and Amy. As if to confirm this, the killer turns in the other direction.
And sees nothing.
We cut back to Amy, still looking behind her. This confirms that she hasn't yet left the tunnel. The killer doesn't see her because he's in another part of the tunnel.
Horror films use such tricks to unnerve audiences, fraying their nerves so they are more susceptible to upcoming shocks and frights.
For more about how horror uses editing, and the difference between shocks vs. frights, see Horror Film Aesthetics: Creating the Visual Language of Fear. This blog represents a continuing discussion of my views on horror, picking up from where the book left off.