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(at around 1h 1 min) Missing from Lindsey (Lucy Liu) and Slevin's (Josh Hartnett's) dialogue about actors who have portrayed the Bond villain Blofeld are Eric Pohlmann, who provided the voice while Anthony Dawson appeared on-camera in From Russia with Love (1963) and Thunderball (1965), and Charles Gray who played the villain in Diamonds Are Forever (1971). Also, Max von Sydow in Never Say Never Again (1983) is not considered part of the James Bond canon as it was a separate production from the official Eon Productions/United Artists/MGM movies.
Josh Hartnett (Slevin) lived with screenwriter Jason Smilovic and his girlfriend in New York City while the script was being written. Smilovic said that he thought of having Slevin wear a towel a lot of the time because he saw Hartnett in one so often. More so, it added a vulnerable quality to Slevin.
(at around 23 mins) According to the DVD commentary with Josh Hartnett and Lucy Liu, Lindsey's reaction when she walks in on Slevin with his towel open is real. The scene was scripted, but Josh Hartnett actually flashed Lucy Liu without telling her prior to filming.
Although meant to be around the same age in the movie, Lucy Liu (Lindsay) is 10 years older than her on-screen co-star Josh Hartnett (Slevin).
Lucy Liu said in a "Making of" featurette that she had more fun making this movie than any of her other movies.
In promotional material for this movie, Sir Ben Kingsley's credit included his knighthood. At first, the actor was singled out for some criticism, as such things are usually omitted from professional credits. It transpired that this was a mistake by a studio executive, who was unfamiliar with the British honors system.