When Oz and Jill are at the café, Oz asks the waitress for a burger with no mayonnaise and the waitress is seen taking Oz's menu. In the next shot, Oz re-affirms to the waitress no mayonnaise and Oz hands her the menu again.
When Frankie Figs and Oz meet up with Jimmy in the hotel room, Frankie hugs Jimmy and he does not have his sunglasses on, the camera shows a different angle of the hug, and then when they return to his face, he does have them on again.
When Oz is trying to talk Jimmy out of killing his wife and Jill is playing with the guns on the table, the position of Jimmy's martini glass changes. From the front, it's sitting on the table, and from behind he's shown drinking from it.
During the sight seeing tour, Jim and Oz are on elevated view of Montreal. In the back ground is a round building, there are two men talking to Oz's right. In the close ups the two men nor the building is seen.
When Oz enters the hotel room, Jimmy is sitting in a chair with his trigger finger indexed along the slide of the gun (as it should be). When the camera angle changes to behind Jimmy, his finger is instantly on the trigger (where it shouldn't be).
Dental records cannot be faked. It isn't just a matter of matching up dental work on a couple of Panellipse films (as shown in the movie). There is also everyone's unique bone density/structure, unique root structure, individual tooth sizes and variations in shape to be considered. These are things that cannot be altered. Moreover, those are the things that they look at when identifying someone from dental records.
While Quebec provincial law requires the English text on any public signage to be no more than half the size of the French text, the bilingual signs with equal-size text are at the airport, which falls under federal jurisdiction.
When Oz is making the dead cop's teeth look like Jimmy's, he forgets to add or pull the upper wisdom teeth. The top x-ray shows 32 teeth, while the bottom one shows just 30 teeth. When comparing dental records this would be an instant dead give away.
When Oz runs into the closed glass door, his hands are raised to stop his face hitting the glass, showing he was expecting the collision.
When Frankie punches Oz in the Hotel room, you can briefly see the padding under Oz's shirt
When Oz is cutting the grass in the scene where Jimmy is taking Oz with him, to go on a "sight seeing", you can see that the "lever" on the top of the handles on the lawn mower is not pushed in. This has to be pushed in for the grass cutters in the lawn mower to rotate. So he is not actually cutting the grass, just pushing the lawn mower around.
None of the people who were shot had blood on them.
When Jimmy, Frankie and Oz are leaving the club and walking down the sidewalk, the crew is reflected in the club's windows behind them.
Sophie is French-Canadian. Rosanna Arquette, not knowing the difference, gives her an accent from France.
Having hired a hit man (albeit an undercover police officer from Quebec who is doing what in Niagara Falls Ontario?) the plan is to drive to Montreal, do the hit, and drive back to Niagara Falls to establish an alibi. Did the producers/directors even look at a map? On a good day, that is an 8 hour drive, one way, on an average day, maybe ten, one way. And that is without comfort breaks or food and gas stops.
When the detectives inform Oz about the bodies found burned in his vehicle, they give him two names. Oz automatically asks if one of the names is the name associated with his neighbor, without inquiring further. A detective would notice this usually and may assume Oz knew more than he was letting on.
As Oz and Jimmy are getting into the car, a boom mic is reflected in the sun-roof.
Oz brushes his teeth almost immediately after he vomits in the hotel room. Stomach acid weakens teeth enamel, and the teeth should not be brushed for at least thirty minutes after vomiting. While this is not exactly common knowledge, a dentist would certainly be aware of the precaution.
When in the jazz bar, as Jimmy Tudeski returns his burger he says, "I'm going to keep the Coke and the fries," just after a server walks by a neon Pepsi sign in the bar. This could be an error by the character, or possibly a mismatch between writing and location choice.