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.
(at around 18 mins) and (at around 1h 8 mins) The same man(black t-shirt, shorts, short hair) walks in front of the police station and the same cop car drives by. Clearly the scene was re-used.
The typefaces in CCTV shots are the same throughout the movie. Although possible, that's extremely unlikely to happen, as are shown recordings from the military, from the zoo and from NYPD.
Early in the film, Sarchie's arm is slashed by Jimmy in an encounter, suffering a deep gash that it is stated will require stitches. In the very next scene at the Bronx Zoo, the wound is not visible. Immediately following, we see him at home and the arm is bandaged.