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 first cut was ten minutes longer and Alejandro González Iñárritu wasn't entirely happy with it. After sharing his doubts with a friend, this one proposed he should show him to the more experienced Mexican filmmaker Guillermo del Toro. After seeing it, Del Toro said to González Iñárritu that he should trim it a little bit, because he saw a great movie that could be a master piece, to which the director argued back. Del Toro then asked permission to make a shorter cut, which González Iñárritu granted. After seeing his friend's cut, the filmmaker agreed with him and made together the final 150 minutes cut.
All the images shown on the TV sets during the picture are commercials. These commercials were also directed by Alejandro González Iñárritu. They include a TV station promotional, an ad for a bank, among others.
The car crash sequence was shot with nine simultaneous cameras, including two on adjacent rooftops and one hidden in a trash barrel. A stunt driver was in the black car, while the model's car contained a remote-controlled animatronic dummy. A practice run caused the black car to accidentally tear the rear bumper off the model's car, but since it was getting late, it was stuck back on and the shot attempted in toto. This time the model's car spun around, overshot its projected target by at least 100 meters, and smashed into a taxicab parked by the side of the road. This take was used in the final print.