For the scenes where the dogs appeared to be dead or dying, the animals were actually heavily sedated under the careful eye of the Mexican SPCA. Multiple dogs that looked like one dog seen on screen were also used, so that the same dog was not under sedation for more than half an hour and not more than once a day at a time.
Controversial because of the fact it depicts dogfights, the dogs seen fighting each other were actually just playing. Careful editing makes it look a lot more vicious. Their muzzles were also covered with very fine fishing line so they were unable to bite each other.
The Red Hot Chili Peppers' music video for their song "By The Way" was inspired by the film's opening car chase scene.
The first film in a loose trilogy of death, all directed by Alejandro G. Iñárritu and written by Guillermo Arriaga. The next two films were 21 Gramas (2003) and Babel (2006). Between them, all three films earned 10 Academy Award nominations.
Shot in some of the more dangerous parts of Mexico City. It was not uncommon for the production crew to be robbed by street gangs.
Alejandro G. Iñárritu: He's a publicist working in the offices where the main character of the second episode works.