Revealing mistake: During the training montage, right as Mac is about to smash the bottle over Charlie's head, you can see Charlie stop what he's doing about a half-second before being hit, and brace himself for the impact, despite not being able to see it coming. This is confirmed on the DVD commentary.
Continuity mistake: In the opening scene, as the gang is being mugged, watch the background. Towards the end of the scene, there are suddenly three cars parked on the street behind the gangs after a brief cut to the mugger, despite there having been no time for them to all appear.
Continuity mistake: When we see Mac and Dennis smash the boards successively over Charlie's back, as the camera cuts to a closeup of Charlie, Dennis suddenly appears behind him, despite the fact he already smashed his board and walked off-camera.
Continuity mistake: When the gang is sitting talking about if Charlie can pull a truck through the snow, Mac has a half full beer. When Dee walks in the beer is 3/4 empty, the shot then pans out and the beer is half full again. (00:01:35)
