When the ultra-shoestring horror film Paranormal Activity was in theaters I didn't get a chance to see it on the big screen. In retrospect, I'm glad my first experience with the movie was at home. It isn't the most frightening, or in any way the most impressive horror flick I've ever seen, but it did do a lot of things right and it pushed certain fear buttons that few movies ever have. The no-frills approach to this single-set, cast-of-four picture is what makes it so chilling. And that's no small feat for a film about demonic possession.

Actors say that comedy is harder to do than drama because it requires them to make people laugh. In essence, it's an art in pursuit of something more visceral than the heady intellectualism of straight stories. In that sense, horror must be the hardest genre for directors, at least to do artfully. Fear is maybe the oldest, deepest emotion in existence, that mindless chemical rush that compels us to run, hide and call for help. Getting an audience that is already predisposed to disbelief to feel genuine fear is a downright herculean task.

Most horror achieves a fear reaction by taking characters out of their comfort zone and dropping them in one variety of hell or another. A good example of this in the recent revival of handy-cam horror is the Spanish instant classic Rec. The protagonists run through an already unfamiliar place avoiding monsters of an unknown origin, with both their hope and their doom connected to the dwindling number of rooms they have to run to.

Paranormal Activity takes the opposite approach. All of the action takes place in a single house that is orderly but clearly lived-in. It's the protagonists' territory, so a lot of the horror comes from the slow but steady breakdown of their home-field advantage. The pacing of the film is deliberate, spending a lot of time getting viewers as comfortable with the surroundings as the couple who live there. When the weirdness escalates to terrifying levels at the climax, nothing about the house has really changed. That ends up being the most frightening part of the movie.

Paranormal Activity is a film about false security. Whether it's the assumption that a man's house is his kingdom or that a person's worldview is unassailable, the movie gets its biggest chills from upending self-assurance. The invisible demon who haunts the unfortunate lovers does little more than mess with the status quo. It may have more nefarious plans for the endgame, but it is content to literally go bump in the night for much of the film's duration.

Just like the experience of the haunted couple in Paranormal Activity, the film's audience is asked to generate as much, if not more, fear from their imaginations as from actual creepy experiences. This makes the movie surprisingly potent for such a limited production. The fear is in the timing and easily the most chilling moments of Paranormal Activity happen entirely off-screen. All it takes is maddening mystery and an enthusiastic scream to elevate a movie to unfiltered horror.