I noticed that during the rehearsal of one particular scene with Faye Dunaway, he looked everywhere but directly into her eyes. He looked at her eyebrows, her hair, her lips, but not her eyes. I didn’t say anything. The scene was a confession by his character that he was hopelessly in love with her, that they came from very different worlds, that he was achingly vulnerable to her and therefore needed her help and support. On the day of shooting we did a take. After the take, I said, “Let’s go again, and Bill, on this take, would you try something for me? Look into her eyes and never break away from them.” He did. Emotion came pouring out of him. It’s one of his best scenes in the movie.
Sidney Lumet, Making Movies.