According to Johnny Depp on the Turner Classic Movies documentary on Marlon Brando, in the scene where he and Brando are sitting at the table talking about the inconsistencies in DeMarco's (Depp) character, when DeMarco admits his father was from New York, Depp's lines were re-written just before shooting the scene, so he had no time to prepare and memorize the lines. So, Marlon Brando talked to the director and cinematographer to find out where the cameras angles were. He then worked out a way in which he cut up Depp's lines in the script and pasted them to the cup of coffee in his hand and then held the cup in his hand in such a way that the camera would not pick up the pasted lines and Depp could read them.
Mike Judge heard a rumor that Marlon Brando and Johnny Depp were both fans of his animated series Beavis and Butt-Head (1993) and at one point, when cameras were not rolling, Brando and Depp were sitting on a couch doing impressions of the animated duo. It is believed that Brando did Butt-Head and Depp did Beavis. At one point, Johnny Depp personally asked Mike Judge if he could play Beavis if a live action movie were made.
When Dr. Jack Mickler takes his wife out for dinner, the woman who was Don Juan's last conquest at the beginning of the movie can be clearly seen, alone and playing with her spoon as she was while waiting in the first encounter.