Paranormal Activity is, as Honest Movie Trailers puts it, a movie featuring a hell of a lot of nothing. The entire movie contains fewer special effects than most chewing gum commercials these days. Yet it beat Saw VI into the ground, and effectively ended the (*mutter* sanctimonious torture-porn) series. People who are jaded with spilled guts and blood were fleeing the theater in terror, and seasoned movie veterans couldn’t watch it at night.
Why does a movie which is essentially a whole lot of nothing inspire so much terror? Because what we see is never as terrifying as what we imagine.