Joel McHale spent months training with knives and martial arts in order to do his own knife stunts in the film. He managed to go through months of training, as well as most of filming without a single injury. However during one of the last days of filming, his son was visiting on set and McHale used his knife to cut a piece of white chocolate for him. He cut his hand and bled profusely.
In the scene where Sarchie and Mendoza are sitting in the car waiting for Santino to come back to the apartment, on the wall behind the car it reads January 4th. January 4th 1967 is the release date of The Doors first album. The entire movie is filled with references to The Doors.
The Latin writing on the wall, "Invocamus te vi ingrediaris ab inferis" means "We call upon you with force to enter from hell". The sentence can also be seen for a few frames in the static at the end of the opening scene.
The role of Butler was always written with Joel McHale in mind, however, Butler was "the worst character in the script", according to the director and writer. After struggling to improve the role, he then imagined what he thought McHale would be like if he had gone to the Army instead of college, and worked in law enforcement instead of entertainment. After that, writing became easier and the character grew.