Revealing mistake: The first morning the new Mrs De Winter is at Manderley, she goes to have breakfast, but when she attempts to pour milk into her coffee, there's no milk in the jug; she's just pretending to pour it.
Audio problem: When Maxim gives Mrs. De Winter the bunch of flowers, right after they are married, she says a few times "lovely", the last time she says it, her mouth is closed.
Continuity mistake: When the girl helps Frank by licking a stamp and putting it on an envelope, Frank gets up from the table, holding two pieces of folded paper in his right hand and goes to the filing cabinet to get a folder out, with the papers still in his right hand. When he goes to return to his seat, the papers are now in his left hand.
Continuity mistake: On the way back from London, Maxim is pretending to drive a right-hand driven car, with Frank beside him, in a studio, with a screen behind them, but when they have body doubles driving in real-life, the car is a left-hand driven car, but only for a minute or two, and then they go back to the studio car.
Visible crew/equipment: In Mrs Van Hopper's bedroom, Mrs Van Hopper is sitting in a chair in the middle of the room and the girl is standing in front of her. Behind Mrs Van Hopper there is a glass-covered picture, a rather large one, and as the camera gets closer to them and up a bit, we can see a reflection moving in the glass. I can't work out what it is, but nothing else is moving, except the camera angle.
Continuity mistake: In the beginning, in the hotel foyer, at Monte Carlo, the girl has a cup and saucer in her lap. When Maxim joins them, the girl is holding the cup and its handle is on the right, then she's not holding the cup, it's just resting in her lap, then she's holding it and the handle is on the left.
Revealing mistake: A lot of "Rebecca" is shot in a studio, even the driving and walking scenes, but in long shots, like when Maxim and Frank are driving back from London, to Manderley, in the "real" shot, you can see it's not Olivier driving the car.
Other mistake: When Maxim and the girl are in the beach cottage after a ship has run aground, Maxim sits in a black chair right next to a lamp that is covered in cobwebs - the place has been empty for more than a year; no-one has cleaned it or been in it, except for Ben, the weird one - but when Maxim sat in the chair, there was no dust rising up and there's not a cobweb to be seen.
Character mistake: In the beginning of the film, in the foyer of the hotel, Mrs Van Hopper takes a sip of coffee and declares it "stone cold." Then she sees Max De Winter and offers him coffee, but all she asks the girl to get from a waiter is another cup, when what they need is another cup and a fresh pot of hot coffee.
Continuity mistake: As the newlyweds are coming down the drive to Manderley, in an open-top car, it starts to rain. But before it does rain, the girl's hair goes from perfect to mussy. Her hair is made to look rained-on before it should.
Factual error: Crawley tells the girl that Rebecca's body was in the sea for two months and Maxim had to identify her, which is totally ridiculous: A body in the sea for two months would have been eaten and nibbled on by everything that eats meat and is passing by; there would be hardly anything left.