Revealing mistake: John Kramer's chain first goes on the side of his stomach, and then it's on his backside... impossible, otherwise the chain would split him. (01:35:47)
Revealing mistake: Boyd brought Dr. Mackles to the location where he escaped the police hunt. Meanwhile, he rummaged through the rest of the place. In a closet, he found a newspaper with an article that talks about the evil South African CEO. In the first paragraph, because the rest is filler text about a completely unrelated topic (the answer about an inheritance question from the advice column of the Moneywatch website). (00:58:50)
Revealing mistake: During the negotiation for the second murder, Happy Anderson writes a "You HOPE she suffered" note, but shreds what looks like a "You HOPED she suffered" note - they are two different handwritten notes. (00:35:00)
Revealing mistake: Ian stands on the rooftop, with an elevated highway to the right of the screen, some distance from the building. The right-side rear view of Ian reveals the elevated highway much closer, practically against the side of the building. The CGI elevated highway's height compared to the rooftop also varies, being lower when Ian sits, and the support posts are not even flat against the underside of the elevated highway. (00:41:54 - 00:42:20)
Revealing mistake: When Jason is getting stabbed to death, there's a quick 2-second shot showing him being stabbed repeatedly in the stomach, with part of his intestines hanging out. But if you pay close attention, there's no actual damage occurring with any of the stabs, revealing it's just an effect. Likely either a collapsible prop knife or a CGI knife being stabbed into him.
Revealing mistake: When Miller is stopped by police and looks into his side mirror, it looks like the police officer is coming out of the passenger side of his car. The front view shows the officer emerging from the driver's side, like he should be. (00:22:00)
Revealing mistake: While inside the tunnel in Rome, before the yellow Fiat makes a U-turn multiple skid marks from previous takes are visible. Though one might pressume that the marks were already there, they are at the same spot and have the same pattern as the skid marks that the cars make seconds later.