"In the editing room, 20 percent of the time you're using stuff from before the actor knew the camera was rolling or you're taking a line from somewhere else and putting it in his mouth"

This quote by Campbell Scott is referring to the modifying process of a movie. He is recommending that when modifying a film, a large portion of the time is spent utilizing video that was taken prior to the actor knew that the cam was rolling. This might be used to record natural responses or moments that the actor may not have actually had the ability to reproduce if they were aware of the camera. Additionally, Scott suggests that often lines from other scenes might be utilized in the star's mouth. This could be utilized to develop a more natural flow of dialogue or to fill in any gaps in the scene. In general, this quote is highlighting the importance of the modifying procedure in developing a successful film.