Typically, an entire dialogue scene is shot at least 3 times: once in a wide shot and once with each actor in close-up. This means the editor has a great deal of freedom to craft the scene. She can show the speaker or listener at any point in the conversation.

Often, it makes sense to see a speaker before he begins to speak. This is called an “L-Cut” because in the timeline, the edit looks a little like a “L.” (see the blue “L” below). Note how the blue guy’s dialogue continues even after we first see the yellow guy. The clip to the right shows you what the timeline below illustrates: an L-cut.  Watch it.