The scene in the coffee shop was improvised. On the DVD commentary, Spike Lee states that when Denzel Washington ad-libbed the line, "I'll bet you can get a cab though," he nearly ruined the take by laughing so loud at Washington's line.
According to Spike Lee, he and Willem Dafoe met in the men's room during the intermission of the play 'Julius Caesar', in which Denzel Washington appears. As they were standing side by side in the men's room, Spike said: "We should work together" and Dafoe replied: "Yeah, Spike, we should" and that was it. Later on, Spike sent him the script.
Spike Lee says that, at the time of making the movie, he was not aware that riddles had been a major part of the plot in another thriller set in New York, Die Hard: With a Vengeance (1995). He said if he had known that he would have cut out the riddle scenes in his movie.
The scene in which the boy shows the video game he is playing on his PSP to Dalton was not in the original script. Director Spike Lee added it to "make a comment on gangster rap's infatuation with violence." The game is not real but was created by an animation house. Lee asked them to come up with animation for "the most violent game ever".
Paul's (Lemon Andersen) line calling one of the detectives that were interrogating him a "wassa-wassa" was improvised. So was Detective Frazier's (Denzel Washington) answer: "Do you know how to say Rikers Island in Spanish?"
The barber in the scene at the exclusive men's club where Jodie Foster confronts Christopher Plummer named Vincent (his nameplate is affixed to the mirror, and Plummer addresses him by name too), is in real life the barber at the Down Town Association on Pine Street.
The line: "Detective First Grade Keith Frazier.....Yesss!!!" is a tribute to New York Knicks former long-time announcer Marv Albert. After a made basket by 1970's New York Knicks star 'Walter Frazier', Albert would say: "Walt Frazier shoots....Yesss!!!"
The shoot-out sequence between the police and the robbers was not in the original script. Spike Lee said he added it because he felt that "it was a good time to interject some action" in the movie. This scene was the last one, it was filmed on the last day so they could "shoot up" the bank movie set.
During the interrogation scenes and when the hostages are being placed on police buses to be taken to headquarters for questioning, the audience learns the real names of Dalton's robber accomplices. 'Steve' is Kenneth Damerjian, 'Stevie' is Valerie Keepsake, and 'Steve-O' is Darius Peltz.
There are several instances of product placement in the film, such as an iPod seen playing propaganda messages, the Dell computer boxes covering the entrance to Dalton's 'cell', Madeline White's Apple Cinema Display and Hermès Birkin Bag, the Sony PSP owned by the little boy, the Chevrolet van used to transport the crew to the bank, and the Volkswagen SUV, which is used to pick up Russell. A North Face backpack was used to carry the diamonds out of the bank. Also, Poland Springs water, Pepsi, and Wrigley's Juicy Fruit are shown.