Continuity mistake: When Ashton Kutcher convinces his jail bunkmate that he is personally in touch with Jesus, by using his journal to cause stigmata to appear on his hands, a stigmata mark can be seen in his right palm before he changes the past (just as he mumbles "tell me if you see anything weird").
Continuity mistake: After little Kayleigh picks up the blockbuster, older Evan is now at Sunnyvale Institution. The blankets are not tucked under the mattress, then they are tucked when he gets out of bed, and in the shot from under the bed, as he searches for his journals, the blankets hang down to the floor, yet in the next shot they are not.
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Continuity mistake: After Evan beats Tommy to death on the college campus, it shows him kneeling over the body, and there is no blood on his collar. The shot changes to Kayleigh screaming, then back to Evan, in the same position, but now with blood splatter on his collar. He had already finished assaulting Tommy, so there shouldn't have been anymore blood spray.
Continuity mistake: When older, armless Evan is sitting in his wheelchair reading the journal entry that says, "Today Mommy is taking me to play with Kayleigh and Tommy." the writing appears to be on the bottom of the journal page. Yet when he goes back to that time, the writing is at the top of the page just as it was in the original scene earlier in the movie.
Continuity mistake: When Evan gets his first nosebleed, during the hypnosis session, the blood on his face changes quite a bit as shots change while the doctor is trying to wake him up. One shot shows two streams of blood, another shows only one, and yet another shows hardly any blood at all.
Continuity mistake: In the scene right after Evan visits Lenny for the first time after 7 years, he is lying on his dorm bed, flipping through his old notebooks. The scene starts out with him biting the nails on his right hand, but in the next shot when the notebook starts shaking, both hands are visibly holding the notebook.
Continuity mistake: When Evan takes Kayleigh (who is now a drugged up hooker) to a diner, there is a plate with a piece of pie, a wallet and a red cigarette lighter on the table in front of Kayleigh. Each time the camera turns to Evan and then back to Kayleigh, the lighter is in a different location. This happens several times.
Continuity mistake: When Evan goes back in time to when they are putting the blockbuster in the mail box, his cigarette falls out of his mouth and onto his shirt. He gets burnt, as is shown when he returns to modern times, but all the rest of the scenes with them in the forest just after it happens, there is no burn mark on his shirt.