Other mistake: Where did those spikes above and below the rear door come from? They exceed the height of the door.
Other mistake: At the end of the movie, when Cory is in Natalie's bedroom, Cory stops and looks at a picture of Natalie and his daughter wearing a high school graduation cap and gown. Cory said his daughter was only 16 when she died so she would've already been dead by the time Natalie graduated. (01:36:00)
Other mistake: When Hercule Poirot is interviewing Mary outside the train, the teapot in the middle of the table has a spout (pointing directly to the right, towards Mary) but no handle on top or the opposite side, towards Poirot, where the handle should have been.
Other mistake: During the opening trap we see Mitch strike the blades with his chain and get yanked forward. However, despite being yanked forward he still manages to stand in line with the others which he shouldn't be able to do, as his chain was shorter due to the extra tug he received. (00:06:30)
Suggested correction: The chain is tugged by the saw blade catching it as it is going round, when it gives loose of the chain, the chain is not any shorter than the others, as the saw blade did the tug not the motor pulling the chain in.
Other mistake: The phone wire was cut in the boy's room when he called his uncle. Yet his uncle used the same phone to make a call just before he died.
Other mistake: The private investigator has a full size Glock. The Glock 21 which is a .45 ACP has the lowest magazine capacity of 13 rounds. The 9mm capacity for the Glock 17 is 17 rounds. The PI exchanges gun fire and after he fires 7 rounds, his gun runs dry. Makes no sense to bring a half empty gun to a fight, plus he just got it back from his brother-in-law. (01:05:00 - 01:06:00)
Other mistake: Derek changed into Tyler's clothes to escape the hospital and take on Tyler's identity. However, it does not look like he remembered to put his blue hospital ID band onto Tyler's right wrist. Hospital bands are usually securely on and not easily removed (or removable without breaking them). When the nurse was removing Derek's (actually, Tyler's) wrist restraints, there was no blue hospital ID band on his right wrist. He asked, "How do I prove to you who I really am?" (No ID band!). (00:21:30 - 00:24:37)
Other mistake: Bo (obviously an adult), who worked with Kevin, was able to walk into the high school cafeteria and take Phoebe into a hallway to talk without any school personnel seeing him or questioning his presence. (00:30:10)