Character mistake: Once Santino and Ares find John again in the hall of mirrors, John is fighting two of the grunt men that came in with Ares and kills them. Both of which had light assault rifles and weapons on them. John and Ares proceed to empty their pistols out at each other before she runs off with Santino. John then throws his empty pistol away and gets up to pursue his target unarmed and while limping. It is unreasonable to think that someone with his skill and training and experience would not take two seconds to reach down and pick up one of the guns dropped by the two men he just killed before chasing after his target, especially given the highly trained body guard with him accompanying his target. As well as probable encounters with more grunts. To add to this, he was seen doing just this moments before when he had limited ammo and each time he'd down a few enemies he would pick up one of their guns and continue. (01:41:30)
Character mistake: Poirot identifies Prof. Hardman's revolver as a 1927 police-issue weapon due to its blued finish and chequered grips. In fact, these features were common in the widely-available civilian versions of the Colt 'Police Positive' revolver and not the least bit specific to police-issue weapons.
Character mistake: Although Henry borrowed two books on crime scene investigation from the used book store, he obviously did not learn enough, especially about forensic science. For example, shooting from the tree house could be determined by the location/slant of the bullet in Glenn's head/body, and cutting off tree branches that would obstruct the line of fire could be evidence of pre-meditation. Henry may have thought he planned the perfect murder, but it was far from that. (00:30:30)
Character mistake: When we see the relative positions Eddie and Johnny have, Eddie appears to be the one that should have done the signaling to the patrol car instead. (00:55:40)