The bathroom scene before the 2nd bar shootout was directed by Antonio Banderas. Robert Rodriguez said he didn't like using 2nd unit crews and Banderas asked if he could direct the scene, to which Rodriguez agreed.
Due to the film's relatively low budget, the same two stunt men were used throughout the movie.
During the production of the film, director Robert Rodriguez and actor Danny Trejo discovered they're second cousins.
The bar in the beginning of the film, where Steve Buscemi and Cheech Marin talk, is an actual bar in Acuna, Mexico called The Corona Club. The bar is a lot cleaner and bigger in reality, but it's like walking right into the movie. They also have quite a few pictures of the cast and crew on the walls.
For most of the killings they used a gun that essentially fired fake blood at the characters instead of squibs. This unfortunately created too realistic of an effect resulting in them having to edit out much of the deaths for the censors.