Continuity mistake: When Diane Keaton and Al Pacino have dinner, he gets up, puts on his coat and sits down again. Now watch Diane Keaton's glass: When the camera's on Al Pacino she's holding the stem, but when the camera's on her she's holding the body of the glass. Another mistake is that at the end of the scene the amount of wine in her glass suddenly doubles.
Continuity mistake: In the first scene, the undertaker Bonasera asks the Godfather for help. When the Godfather gets up from his desk, the rose in his lapel is either fresh and straight or slightly wilted and bent in alternating shots. Also, later in the wedding scene, this rose keeps recovering from intermittent spells of withering.