Continuity mistake: Michael Douglas is going home to Mount Kisco the very very long way down Riverside Drive South. Again Alex's tape hasn't skipped a beat.
Continuity mistake: When Michael Douglas is listening to Alex's tape it's midday when he enters the East River Drive underpass and comes out the sun has clearly set. Alex's tape doesn't skip a beat. (01:17:00)
Continuity mistake: When Michael Douglas puts on his headphones to listen to the tape in his den, he puts the headphone with the cord on his left ear. When his wife startles him the cord is on his right ear.
Continuity mistake: When Dan throws Alex into the bath, she goes in face down, but suddenly she is face up - which would be a difficult manoeuvre in a small bath.
Continuity mistake: When it looks like Alex is dead in Dan's bath, she has a long strand of blood coming out of her mouth, but a second later it's gone, and her eyes, which were white, are no longer white - they are open and look like normal eyes.
Continuity mistake: When Alex, naked in bed, jumps up to stop Dan leaving, she attacks his shirt, and you can hear it ripping, but, later, it's completely fine - no ripped bits anywhere.

Continuity mistake: When Dan leaves the budget office in his rental car, the front license plate is mounted off to one side, unusual for this type of vehicle. When he arrives at the house, it's still the same license plate number, but the plate is now mounted on the centre of the bumper.
Continuity mistake: When Dan's wife is by the dinner table talking about the house, his arm is up, yet a frame later from a different angle is down.
Continuity mistake: In the elevator scene as you look down the shaft from above, the air is crystal clear with no smoke in sight. Then in a few seconds smoke appears near the windows but in the next shot when the elevator stops the smoke is gone. (00:20:10)
Continuity mistake: In the scene where Beth is desperately trying to find Ellen, she approaches a stopped Chevrolet Caprice wagon and rear ends it. When the camera switches to an interior shot of Beth's vehicle during the collision, the vehicle in front has changed to a Ford LTD wagon.
Continuity mistake: While eating together, Alex tells Dan that she stood up her date, and raises her hand. From the opposite angle it's lowered.
Continuity mistake: When Dan and Alex are under the rain, a black man in a gabardine passes by Dan, and a frame later passes by Alex, in the opposite direction.
Continuity mistake: Dan is having a drink with Alex and he talks about his parents' divorce. His glass swaps from being on the table to in his hand between shots.
Continuity mistake: After Glen Close kicks Michael Douglas out of her apartment he's standing next to her bicycle holding his stuff. It can be assumed that he put the stuff on the bicycle seat because in the next shot his hands and the handlebars are empty. But later as we see him getting ready to leave again his stuff is the on handlebars. (00:34:35 - 00:37:10)
Continuity mistake: When the little girl is playing in the back yard outside the rabbit cage it's winter, not a leaf in the tree she is under. In the very next shot as they get into their car all shrubs and trees in this shot have their leaves. (01:23:10)
Continuity mistake: When the phone rings as Beth paints, Beth puts her roller in the tray and goes to answer the phone. When she returns the roller is in a different position than it was before.
Answer: So her parents (especially her father) would go through hell, not knowing where she was or if she was safe.
Brian Katcher