Michael Cain has said that early in his career he once held Sean Connery's hat while he fought and beat four men in a nightclub single-handedly. This may be the inspiration for the scene in which Robert Duvall's character also fights and defeats four men single handedly while Cain and Osment watch.
In each scene with Detective Donald Kimball (Willem Dafoe), Mary Harron asked Dafoe to portray his character three different ways: 1) Kimble knew Patrick Bateman killed Paul Allen, 2) Kimball didn't know Bateman killed Allen, and 3) Kimball wasn't sure if Bateman killed Allen. Harron would then edit the takes together, giving the audience an unsure vibe of what Detective Kimball thought of Bateman.
Anthony Hopkins stated that one of his goals in playing Hannibal Lecter for a final time was to re-establish that he is an evil serial killer, as Hopkins believed Hannibal had come to be seen too much as a likable anti-hero by audiences.
When Lester throws the asparagus, he was supposed to throw it on the floor. The reactions of Annette Bening and Thora Birch are genuine.
It took around 120,000 syringes to complete the needle pit sequence and It took four people four days to replace all of the needle tips with fiber tips.
The hunter who shoots Bambi's mother was originally going to be included as a character in the movie. But, for a man to shoot the mother of the hero, he would have to be clearly cruel and villainous for children to accept him. Since Walt Disney didn't want to be seen as maligning hunters as evil, the character was cut and never shown in the final version of the film.
The featured performance of Robert Newton as Long John Silver is so iconic that it is thought by many to be the origin of today's stereotypical "Arrrrr"-laced pirate patois. (most notibly Geoffrey Rush's "Barbossa" character in the Pirates of the Caribbean movies)