'I was blown away and also scratching my head,' recalls DP Wally Pfister of seeing zero-gravity sequence in the script.

On the red carpet for "Inception" last week, star Joseph Gordon-Levitt talked at length about one of the film's most eye-popping visuals: a zero-gravity fight scene in a dream-created hallway that spins in all directions. It's an astounding bit of moviemaking magic that has you wondering just how director Christopher Nolan and his team were able to do that.

We put that question to Nolan's right-hand man and longtime director of photography Wally Pfister, who revealed the inside scoop about the hallway scene, describing it as the movie's most technically challenging sequence.

"There are always scenes in a Chris Nolan script where I'm wondering how we're going to pull it off, going all the way back to Guy Pearce shooting Joe Pantoliano in the head in 'Memento,' " Pfister told MTV News. "When I was reading those rotating hallway scenes, I was blown away and also scratching my head," Pfister recalled.

To create the environment, the scene was shot using not CG effects, but rather massive, rotating sets that twisted and turned and forced Gordon-Levitt to maneuver with utmost caution. Five-hundred crewmembers were involved in the scene, which took a full three weeks to complete. In a World War I-era airship hangar just outside London (also home to sets for "Batman Begins" and "The Dark Knight"), Nolan's crew built a series of different hallway settings: a horizontal one that rotated 360 degrees, a vertical one that allowed actors to wear wires and another on which the actors were strapped to steel trolleys, which were eventually erased using visual effects.

Gordon-Levitt trained for two weeks with the stunt department to learn how to negotiate the rotations. When it came time to shoot, the whole crew would rehearse first with no rotation, and then graduate to a slower rehearsal with a little rotation, until it was finally time to roll the cameras.

"We run the fight scene for as long as the actors can pull it off," Pfister explained. "We begin with a camera that's not fixed to the set and shows a bit of the rotation, and then you quickly jump to where you're rotating with the set. It creates this bizarre, strange movement. It's an exhausting process for the actors. Having rotated on that set myself, it's really quite challenging and a very strange thing to get used to. If you jump at the wrong time, you could be falling 12 feet through the air.

"We kept coming back to it," he added. "We'd shoot out a part of a sequence and then the riggers would have to adjust something. We'd duck out and shoot something else and come back a few hours later and shoot more. The whole thing was spread out over about three weeks. You've never seen anything like this before."

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