Revealing mistake: When Rachel has a red turban on and is supposed to be bald, you can see her hair under the turban.
Revealing mistake: Throughout the movie, we are reminded repeatedly that Harrison and Travis are naive 9-year-old boys who have absolutely no knowledge of guns or gun safety. Near the end, when the two boys are trapped in the backseat of the cop car, they clumsily try to blow out the window with a 40 caliber semi-auto handgun, but they can't even figure out the safety mechanism. When they do release the safety moments later, young Travis suddenly takes aim and fires with a perfect two-handed forward presentation. We see the gun and Travis's hands in close-up, and he's properly holding the semi-auto with trained dexterity just before it fires. This appears to be a skilled stand-in firing the gun.
Revealing mistake: In the flashback of the death of Noah's parents, besides the obvious clichè of insta-explosion on impact, it's obvious in the second shot that the car is exploding from within the passenger seats. (01:09:55)
Revealing mistake: When Victor arrives with the drum he says is full of jet fuel, it's very obvious the barrel is empty by the way he's handling it.
Revealing mistake: When Sam phones his car, as he and Kate are hiding in Talbot's apartment, it is discovered that the two people sitting in Sam's car have been killed by the Watchmaker. One of the dead bodies is shown blinking in the shot.
Revealing mistake: From the sound made when the car hit the deer, as well as the deer's overall appearance, it was obvious the deer was fake. The fake deer's body was almost uniformly brown, but the "dead deer" on the road had a white underbody that went part way up its side and along its legs, which should have been visible on the "fake deer." (00:10:19)