Actor Allusion: Philip Chan, who played Superintendant Pang, was a CID cop in the '70s and for a while was the head of one of the first undercover units of the Hong Kong Police.
Creator Backlash: Anthony Wong wasn't happy with the film as he thought that his character, Johnny Wong, was a two-dimensional and thinly characterized villain. He also considered Woo hard to work with.
The Danza: Anthony Wong plays Johnny Wong, the film's villain.
Trash the Set: The teahouse that served as the setpiece for the first big shootout of the film had been slated for demolition, and John Woo got permission to use the teahouse for the shootout in question.
John Woo originally intended for the film to be less stylized and more gritter than his past works, citing the Dirty Harry films as inspiration. Michelle Yeoh was to play Tequila's partner on the force, and Tony Leung Chiu-Wai was picked to play the villain, a psychopath poisoning baby formula. Woo was talked out of the idea, and a new plot was written with Tony Leung Chiu-Wai playing an undercover cop.
A number of story elements were improvised during filming and not part of the original script, such as the character of Mad Dog, who came about as Woo felt that Johnny Wong didn't pose enough of a physical threat to the other characters.
Around a half-hour of scenes were cut during filming, among them were a relationship sub-plot between Teresa and Tequila, of which there's a few bits left over in the final film. Due to these cuts, Chow Yun-Fat felt his character was not as deep as Tony Leung Chiu-Wai's, and convinced Woo to play a mentor character to Tequila.