The scene in the bathroom bar where Robert De Niro dunks his head in a sink full of ice, is in fact a real trick that real like police detectives use to get over hangovers. De Niro discovered the trick during his research for the role and was eventually written in.
Graham Knuttel, the Dublin-born artist, was paid £50,000 for a canvas which was destroyed in the film. The producers wanted the movie to be as realistic as possible, and so ordered the artwork to be destroyed in one scene.
The language spoken by Charlize Theron's character is Afrikaans, one of the official languages of South Africa. She says, "Hello Mr Botha, can I call you back? You would never believe who just walked in here, it's Eddie Flemming. Thank you, good bye." Botha was a famous boxer in the 90s from South Africa.
Mindy Marin who's the film's casting director was featured in the part of Kim Cattrall's assistant because she looked the part and they weren't able to find an actress who was capable of playing the role prior to shooting according to director John Herzfeld.
Edward Burns gained 20 lbs for the movie to accurately play an arson investigator as they have to have spent at least 7 years in the fire service and would gain muscle mass across their backs, chests and arms.
There are a lot of location inconsistencies throughout the film. Like the scene involving the apprehension of the Jamaican killer that Robert De Niro and Avery Brooks are going after early in the film was clearly Los Angeles and most of the scenes in Times Square that were shot in New York for example. Most of the interiors were shot on sound stages and actual New York and Los Angeles locations.
While the film was delayed, J. Peter Robinson was brought on to provide a new beefed up original score for the film as the studio was not happy with what 'Anthony Marinelli' had done musically for the film at that point. Marinelli had written about seventy minutes of music for the film. Robinson composed approximately thirty minutes of new material and retained about half of Marinelli's contribution which is why they share composing credit in the final credits for the film.
The tension between Emil and Oleg is based on the real tension between some Czechs and Russians. Many Czechs hate the Russian language as they were forced to learn Russian under Soviet occupation. Karel Roden refused to speak Russian to Oleg Taktarov during rehearsals.
The film was originally slated to be released in the Spring of 2000 by New Line with theatrical trailers appearing in the fall/winter 1999. For reasons unknown, the film was pulled from the Spring 2000 schedule and then delayed. The film was finally released in March of 2001. A similar situation would happen with Knockaround Guys which was slated to be released that Spring only to be yanked and delayed. That film would finally be released in late 2002.