Revealing mistake: Throughout the entire film, it's quite obvious that most of the "snow" is fake. It just doesn't quite look right. It often resembles mashed potato flakes or Christmas tree flocking instead of real snow.
Continuity mistake: When Sam walks into his kitchen at the beginning after cleaning his driveway, he walks past his son. His son goes from having his right hand down on the counter to up, holding a ladle between cuts.
Revealing mistake: When Jack is melting after being showered with acid, at one point, there's a very obvious cross-dissolve used to blend two shots into one as Jack is reduced into a skeleton. It almost works, except suddenly, the snow around him is slightly different. (Some impressions into the snow and whatnot appear during the fade that shouldn't, as does a few pieces of debris.)
Revealing mistake: When Jack is being showered with the acid, you can tell that they had the actor lying down, dropped the liquid on him from above, and simply tilted the camera onto its side. The way it sprays "sideways" is incredibly unnatural.
Revealing mistake: In the beginning, when Jack kills the guard then puts the cigarette out on his face, watch closely. As the camera pans down, you can see him starting to switch the lit cigarette in his right hand with an unlit cigarette hidden in his left hand so he doesn't actually burn the actor playing the guard when he "puts it out" on his face. It can be hard to notice at first, but once you see it, it's super obvious.
Revealing mistake: At the very beginning of the film, we see the transfer vehicle carrying Jack driving down the road. You can tell in several shots that the (fake) snow isn't really falling, but is just being blown in front of the camera from off-screen, especially since there's no snow hitting the road, and it's coming from the side, not above.
