Eli Roth has the well-deserved reputation of being the king of splatter, after having directed 2002's "Cabin Fever" and 2005's ultra-gory "Hostel." "The Last Exorcism," which opens today, represents a big departure for Roth, who serves as the film's producer while Daniel Stamm directs. There's blood, of course. But that's not the focus. Instead, "The Last Exorcism" is an exercise in creating tension.

Much of that tension comes from the creative use of the camera. "By using the camera as a character, we eliminate the fourth wall," says Stamm, refer

ring to the imaginary boundary between a fictional work and its audience.

"It brings the viewer into the frame," Stamm says. "It gets the audience involved. And the camera is the voice and eyes of the audience."

The viewers are acutely aware of the camera from the first few scenes, when the Rev. Cotton Marcus (Patrick Fabian) speaks to it, detailing how he plans to expose the fraudulent practices of exorcists. He has been performing such rites in Louisiana for more than 20 years, he says, and now he's ready to confess his sins and show the tricks of the trade.

So the camera follows the preacher to a farm where a teenage girl named Nell Sweetzer (Ashley Bell) is suspected of slaughtering livestock during nightly demonic possessions. At least that's the contention of the girl's fundamentalist father, Louis Sweetzer (Louis Herthum).

The camera chronicles the initial meetings, and everything seems to be setting up the notion that you're watching a documentary, which has been edited into a feature film from hours and hours of footage. And there's no question that the preacher is in control, that this is his show — that his movements drive the movement of the camera.

But then the control of the camera begins to shift, and with that loss of control comes the tension. Audiences might feel safe without the so-called fourth wall in a documentary. But it's another matter when the fourth wall is eliminated in horror.

"It makes the audience feel like they're losing control, just like the characters onscreen are losing control of the situation," says Stamm, who visited Austin last week with Roth. "Trust is being subverted," and the movie begins to shift from faux documentary to horror.

But even then, the audience can't be sure of where the horror is headed. "We wanted to make a movie that wasn't like the usual horror movie," says Roth. "The story exists in the world of a psychological thriller about a girl who might be possessed or seriously psychiatrically ill."

"There are multiple levels of tension," Roth says. "But either way, Nell (the teenage girl) is in trouble, possessed or insane."

Stamm says the goal was to keep the audience guessing. "The movie has to be one step ahead of the audience and play off that unpredictability," he says.

The technique is the cinematic version of the so-called unreliable narrator in fiction.

"It's a paradox, really," Stamm says. "You think that what's happening on camera is a recording of the truth," much as you might be inclined to believe a narrator in a novel. "But the camera's vision is limited. It's not 360 degrees. And what you think might be true might not be."

The ultimate loss of predictability occurs when the unseen man behind the camera in "The Last Exorcism" finally screams in frustration: "Let's get the hell out of here." And the movie begins to spin out of control, both figuratively and literally.

"It's well framed and progresses to the point of falling apart," Roth says. "We're not pretending it's real at that point. It's anything but that. But it puts you as close to the subject matter as possible."

Much of the credit for the film's success has to go to the screenwriting team of Andrew Gurland and Huck Botko, whose 2004 comedy "Mail Order Wife" used a faux-documentary approach.

But the realistic feel also comes through the performance of Bell as the troubled teen.

She seems passive, even almost angelic, in the early scenes. But Stamm opts to skip computer-generated effects as the film progresses and have Bell do all of the twisting and stunts during her violent episodes. When you see the vessels bulging in her neck, they really are bulging.

"All of his helps make the movie more believable," Stamm says.

It also makes "The Last Exorcism" much more scary.

cealy@statesman.com; 445-3931