Audio problem: When John rips the phone out of the wall, when it hits the floor it makes a bell sound even though its a cordless phone.
Other mistake: John explains to his friend Ed that, within the last two weeks since the accident, Mary has undergone brain surgery to remove the tumor in her right temporal lobe and that she is undergoing chemotherapy. This surgery alone would necessitate shaving at least half of Mary's head, and the chemotherapy would prevent her hair from growing out again for months. But, in the immediate next scene, we see John at Mary's side as she recovers in the hospital, and her red hair with natural hairline is as full and lush as in the beginning of the film.
Revealing mistake: When John goes to close Gordon's eyes, as he lowers his hand, you can see him close his eyes on his own.
Plot hole: In the scene where Richard Gere is looking at his reflection in the motel bathroom mirror, he imagines smashing his face into the mirror. When the phone rings, breaking his hallucination, he still has blood on his hands but it is never addressed.
Revealing mistake: Near the end after Richard Gere jumps in the river to save Laura Linney, the water is shown to be very deep. When Gere reaches the police car, it doesn't appear to be that deep in at least one shot.
Factual error: At the end, it says the cause of the collapse has never been determined. It was caused by the failure of an eyebar in a suspension chain. Also due to too much weight on the bridge.
Continuity mistake: In the bridge collapse towards the end of the movie, John's gloves are on then off then on again.
Continuity mistake: John's shoes change from the time he gets out of his car the first time at Gordon's house to when he's inside the house in the bathtub.
Factual error: John supposedly goes to Chicago to talk to a mothman expert, but it shows the two of them walking into The Mellon Institute which is actually in Pittsburgh.
