Go to the bathroom before seeing this one.

Paranormal Activity is the little movie that snuck into town in October 2009 and made everyone pee their pants. I saw it with a fairly large audience and I suggest you do the same because audience reaction is a big park of this movie's experience.

The movie starts fairly slowly as we are introduced to Micah and Katie, a young couple living together in a house in San Diego. Nice house, even has a pool. He's a day trader and she's a student. He's kind of immature and full of himself. She's introspective.

As everyone knows by now, this is a "found footage" movie a la Blair Witch Project as we see what Micah's video camera picks up over the course of several days as he tries to document the ghost or demon that has been bothering Katie since she was 8.

The camera rolls while they sleep and we see little things. A door moves a couple inches. Another night, a light goes on the hallway, then goes out. Then, more happens. A whole lot more.

The movie is almost entirely Micah and Katie. She has a girlfriend who drops in. They invite a ghostbuster-type psychic, who totally wimps out and hightails it.

The movie has a kind of pulse -- safety during the daytime awake scenes, followed by excruciating tension during the sleeping scenes when you have no idea what you will see or hear.

Whatever is haunting Katie is attached to her, not the house. So moving would not solve the problem. As the movie progresses, fear turns to terror and she becomes all but immobilized.

As the jump moments built and built, the audience moaned and yipped. A few screamed out loud. The final 10 minutes had them gripping their armrests.

I have learned that three different endings were shot. No doubt they all are included on the DVD. As for the one used, it delivered the movie's biggest shock and it sure worked for me.

As we filed out of the theater, one teenage girl, visibly rattled, said she was sure she would not be able to sleep that night.

This is an instant classic, destined to take a place at or near the top of the list of the most frightening movies ever made.