Deliberate mistake: The chainsaw cuts off the German torturer's leg and it manages to move all by itself a few feet within a few seconds, when it would just run and slowly move and stall as seen after it moves. Obviously done to increase the tension. In addition, the chainsaw looks very clean with no blood dripping and bloodstains on the floor.
Deliberate mistake: When Nico finds Hilda's body at the start of the movie, her left arm is shown next to her body, and her right arm is outstretched. When her death is shown later in the movie, both arms are outstretched when she lands on the floor. (00:05:50 - 01:30:55)
Deliberate mistake: How does Lisa appear resplendent in that perfectly smooth wrinkle-free negligee when we saw it earlier all stuffed into her overnight bag?
Deliberate mistake: The agent is entering the office approaching his desk where a computer sits with the screen on depicting classified material. Computers left unattended go dark after x amount of time. This computer being in a federal FBI building should be logged out of and not open for everybody to see. (00:19:00)
Deliberate mistake: During his autopsy in Saw IV, it is revealed John Kramer was 52 at the time of his death. Kramer's role in this film is the very early stages of his time as Jigsaw, shortly after his cancer diagnosis, which would put him in his early 50's. However, he looks far too old to convincingly be that young (Tobin Bell was in his mid-70's at the time of filming). He even looks older than he did when he was on his deathbed in Saw III.
Deliberate mistake: Poirot riles up Pennington narrating the story of Grand vizier Ptahhotep who was crushed under the weight of the silver he embezzled. It's a lovely moral story, but Ptahhotep was actually a virtuous administrator and is credited (with various caveats) with writing "The Maxims of Ptahhotep", one of the first books in human history, and there's no record of such a story. It's likely that Poirot made that part of the story up counting on Pennington's ignorance on the subject. (00:44:20)
Deliberate mistake: Wyatt is killed in a park next to El Prado museum (which can be seen in the background). Then S and McQuarry cross the street and appear next to where the bank was. This speeds the pace of the movie, but truth is that the building of the bank and El Prado are 20 minutes walking distance away from each other.
Deliberate mistake: When Willy's fellow prosecutor, Norman, dropped the Crawford preliminary hearing on him, they said it started at 15:00. Willy is in a rush and the whole ordeal takes him just a few minutes. Still, when Nunally accosts him in the parking lot, the movie sped things up; it's nighttime. (00:27:00)