Revealing mistake: When the one man drops the toilet from the top of the building onto the Russian guy, as the toilet smashes over his body, you can tell it is obviously a fake breakaway prop, as the pieces of it are all practically paper-thin.
Other mistake: In the scene when the brother is calling the number on the Russian's pager, he writes down the name of the hotel before you hear the Russian say the name over the phone.
Continuity mistake: In the scene where the brothers kill the mobsters in the hotel, when they are shooting the men on the counter in the back there is no case visible, but in the scene where the brother find the case of money it is there when they find it.
Continuity mistake: In the scene where Agent Smecker is doing a gunpowder residue test with liquid paraffin, his left hand starts off on the corpse's wrist, then in the next shot, Smecker's hand is by his chin. In the next shot, it is back on his wrist. In the last shot his hand is back by his chin. (00:12:31)
Factual error: In the scene, where Paul Smecker is checking the green trash-bin, he finds a bullet from Ivan Checkov's gun. Nevertheless, earlier (in the plot), or later (in subsequence of the scenes), in the scene, where Connor MacManus is falling down with toilet on Russians' backs, Ivan Checkov, while the toilet hits his bald head, is shooting with his gun, but he misses the trash-bin - the angle of shooting is obviously too extreme to hit the bin. (00:23:34)
Other mistake: In the scene at the bar when the Russian gangsters arrive, Ivan speaks with a heavy Russian accent. In the scene directly after the bar fight, after he kicks in the door to the apartment, Ivan yells his first 4 lines with no accent. (00:07:20 - 00:20:40)
Continuity mistake: After the bar fight, one of the brothers pulls off the toilet and throws it from the roof. But if you compare where he throws it from, to where it hits the people, it doesn't make any sense, the angles just don't work out.
Revealing mistake: During the scene where Connor is writing down the name of the hotel, you can see his Veritas tattoo smearing.