One of the most memorable moments from The Godfather is when Vito Corleone (Marlon Brando) slaps Johnny Fontaine (Al Martino) around the face and tells him, "You can act like a man!" after he starts whinging about not getting a movie part that he desperately wants. This was all on Brando; the famously eccentric actor decided that he wanted to bring a little more life out in Martino's performance, and so completely out of the blue, slapped him around the face. Watch Martino's face carefully; he clearly doesn't know how to react, but well aware the cameras are rolling, at least maintains a measure of shocked composure that transpires quite hilariously into one of the movie's best scenes.