The chainsaws in the movie were not on for the fight, but actually had incense inside them to make them look like they were smoking.
In one scene, Chow Yun-Fat tells a receptionist that his name is Mark Gor. Mark Gor is the name of a popular character he played in A Better Tomorrow (1986) (A Better Tomorrow).
In the beginning of the film, Shing Fui-On and Chow Yun-Fat talk about being from the Hakka district of Hong Kong. Chow himself is from Hakka.
The list of names that Francis reads out as he fills up the glass with raw eggs is a play-on-words of the Cantonese word "lung" (dragon). Every single person he listed out contains "Lung" somewhere within their professional name: Bruce Lee (Lei Siu-Lung), Jackie Chan (Sing Lung), Alain Delon (Ah Lan Daai Lung), Sylvester Stallone (Si Taai Lung) and Ti Lung. As two added notes, not only is the egg-eating scene a reference to what Stallone did in Rocky (1976), but also Ti Lung has a small role in this movie.
The scene in which Francis beats up Marydonna is one that even Chow Yun-Fat objected to taking part in, but the scene was put into the movie because it played well to local audiences in Hong Kong at the time. Nina Li Chi, who played Marydonna, was deemed by the Hong Kong public to be quite arrogant and that she could not speak Cantonese very well (she spoke it with a "Shangahinese" accent, according to Bey Logan's audio commentary on the UK Hong Kong Legends DVD release). This scene was deemed to be an on-screen "dig" at her perceived personality that she reportedly exhibited at the time.