Doctor Strange hit theaters and was tops at the box office over the weekend, and Yahoo Movies’ own Khail Anonymous sat down with the film’s director, Scott Derrickson, and talked about just how difficult it was to shoot that epic reverse fight scene.

“It was so difficult, I mean, it was a concept to start with,” Derrickson said. “You know I said I want this final battle scene to be one where you know characters are fighting forward in time but everything is un-destroying itself in reverse time.”

So, how did they manage to shoot the ‘unshootable’ reverse fight scene? “We figured it out. Every shot had to be shot four or five times, Derrickson said. “We had to use what’s called Motion Control, so it’s time-consuming. Specialty frame rates and then Reverse Its. Then layer it again and add layers of debris. It was so complicated.”

See how Doctor Strange did at the weekend box office:

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