This opens up an important area. When the actor is being photographed looking at someone off-camera, he can obviously see past him to the whole darkened studio. We call this the actor’s “eyeline.” It can involve both sides of the camera. Just before we roll, any well-trained AD will always say, “Clear the eyeline, please.” If William Holden is making love to Faye Dunaway, he doesn’t want to see some teamster sipping coffee behind her. He doesn’t want to see anybody other than Faye watching him, even if he has great concentration. Since most crews don’t understand this, “Clear the eyeline” becomes a never-ending refrain.