BY GLENN WHIPP >Film Critic

At first glance, "The Happening" seems like a retrenchment for filmmaker M. Night Shyamalan following the critical and commercial disaster of his last movie, "Lady in the Water."

But there's this: Even though "The Happening" shares the spooky nightmare vibe of "The Sixth Sense" and "Signs," both the action and atmosphere here are much more intense. It's Shyamalan's first R-rated feature, and judging from the way he's talking about it, it won't be his last.

"This is probably the most fun I've ever had making a movie,"

Shyamalan says. "It was great not pulling any punches."

The movie, which Shyamalan calls a cross between "The Birds" and "Invasion of the Body Snatchers," follows a high-school science teacher (Mark Wahlberg) trying to escape a "force beyond our understanding" that seems to be environmental in nature. (The movie's original title: "The Green Effect.")

As per usual, Shyamalan is reluctant to reveal much in the way of details about the film itself. As for the experience of watching the movie, he's more than happy to expound.

"People who have seen it have a physical reaction to the movie,"

Shyamalan says. "Muscles contract. People tell me, `Oh, my God, I'm sore,' when the lights go up."

Just don't expect buckets of blood. Shyamalan believes horror scenes are more effective when they're elegantly shot, juxtaposing form and content. He doesn't want to repulse you. He would like to instigate a nightmare or two.

"It's all about going through an experience that isn't safe, and coming out tattooed by that process," Shyamalan says. "To me, that R rating is an emblem of the film's intensity. There are plenty of PG-13 movies this summer. This movie, you're coming to see something visceral and intense, like the first `Alien.' It's not safe, nor should it be."

>Glenn Whipp