Four live octopodes were eaten for the scene with Dae-su in the sushi bar, a scene which provoked some controversy abroad. Eating live octopus in Korea is commonplace although it is usually sliced first. When the film won the Grand Prix at Cannes, the director thanked the octopodes along with the cast and crew.
Scenes at the police station with drunken and disorderly Dae-su Oh were the very last scenes the director scheduled to film. Min-sik Choi (Dae-su Oh) ad-libbed most of these "drunken" scenes, including the scene of him playing with toy wings that he bought for his daughter. He also ad-libbed many of his lines during the penthouse scene, including the anthem of his school.
Dae-su Oh bangs his head right after stopping Mi-do from reading his diary. This "head banging" was not a scripted action. However Hye-jeong Kang (Mi-do) kept her cool and continued on with her lines. The director, in an interview, said that he kept and used this supposedly NG scene for its comical and emotional value.
The restaurant that Mido works in is called "Mediterranean", which is the name of the restaurant in real life, but the director originally intended for it to be called "Akira" - not as a reference to the popular Manga, but to the Japanese director Akira Kurosawa.
The telephone number (08-6600330) which is supposed to go to Oh Dae-su's daughter's foster parents home in Sweden, actually has been "shut down requested by the owner of the number" (that's what the voice says when you call the number). But you are referred to another number (08-54589400) which goes to "The Embassy of the Republic of Korea" in Stockholm, Sweden.
This is the second one of director Chan-wook Park's "Revenge Trilogy". The first is Sympathy for Mr. Vengeance (2002). The third is Sympathy for Lady Vengeance (2005). Incidentally, the very first speaking character in this film, who commits suicide with his dog and whose story we never hear, is played by Kwang-rok Oh. In the first of the revenge trilogy he played an anarchist who appears at the very end of the film. He is the only credited character who appears in both movies.
Chan-wook Park wanted a documentary feel during the police station scene by using jump cutting. As a result, most of Min-sik Choi's ad libbed lines were trimmed. The full ad libbed scenes are found on the UK Tartan DVD.
During the scene in the cyber cafe, the extras in the background are playing the popular first person shooter Half-Life: Counter-Strike (2000). This is apparent when watching screens and when listening to background noise. You can faintly hear the famous AWP weapon being fired from time to time. You can also notice sounds from StarCraft (1998) in the background.
The trivia items below may give away important plot points.
The famous one-take corridor scene was shot in three days. No CGI was used to cleverly edit the sequence like a single shot but the scene was actually shot in one take (although a little CGI was used to show Oh Dae Su getting stabbed in the back with a knife and to correct some punches landing).
The last scenes of the movie (with snow and footsteps) were filmed in New Zealand. After the ending credit completely rolls over, audiences can hear sound of the wind. It was actual sound of the wind recorded in NZ location. The director revealed in an interview that he was impressed by the scenery of NZ so much he saved the sound there for the (Korean) audience.
The phrase "Like the gazelle from the hand of the hunter, like the bird from the hand of the fowler, free yourself," which was a clue to Woo-jin's residence, is actually from Proverbs 6:5 NOT Proverbs 6:4. The director once said that it was just a hoax, not a mistake.
The mountain at the final scene is Mount Tinline and it's shot from Mount Lyford in July, 2003. Film makers and the local film crew came together for 4 days, set up a camera crane and a slider at Mount Lyford, west of Kaikoura in the South Island of New Zealand. The exact coordinate of where Mi-do and Dae-su stand in front of the sunset behind the mountain is (42° 26' 48.00" S, 173° 08' 13.00" E).
Despite the movie's depiction of graphic (but mostly offscreen) violence, only seven characters die on screen (some of the prison guards Oh Dae Su beat up in the one-take corridor scene appeared at Mi-Do's apartment with Mr Park joining them): The suicidal man at the very beginning, Joo-hwan, two of of Woo-jin's enforcers that Oh-Daesu kills in his final confrontation with Woo-jin, Mr Han, Woo-jin Lee and his sister. The number of deaths in total offscreen and on screen might be higher due to Oh Dae Su's family murdered and the the prison guards who fought with Oh Dae Su in the one-take corridor scene who died of their injuries.