Crew or equipment visible: Camera dollying back from Mrs. de Winter sitting on a chair brushes some flowers on a table.
Errors made by characters (possibly deliberate errors by the filmmakers): When de Winter is showing the honeymoon film, he tells Mrs. de Winter "this is where I set the camera up on the tripod". However, the image they're watching zooms in (this is before the cinematographic image zooms in on the entire film-viewing scene in the movie, itself). Since the camera was on a tripod, it wouldn't have been able to zoom by itself since de Winter was posing with his wife at the time, not adjusting the camera.
Audio/visual unsynchronized: When The Second Mrs. de Winter and Maxim marry, he gives her a large bunch of flowers. She repeats "Perfectly lovely", but the second time, her lips do not move.
Continuity: After the luncheon, de Winter and "I" are standing on the steps waving goodbye, Jasper the dog moves from one side of the steps to the other between shots.
Continuity: When the new Mrs. De Winter first enters the room to do her correspondence, there are three books on the table. An establishing shot shows that the book on the left is labeled "menus", and the one in the center is labeled "addresses". Mrs. de Winter picks up the one on the left, and it is now revealed in a close-up to read "addresses" on the cover.
Continuity: Frank's hand holding the letter jumps from in front of the filing cabinet to resting on top of it.
Continuity: During the dining scene after the second Mrs. de Winter knocks over the vase, the neckline of her blouse goes from untidy to perfectly neat between shots.
Revealing mistakes: Walking back from the beach, the background moves much more quickly than the characters.
Continuity: In the Monte-Carlo Hotel Lounge, the 'girl' and Mrs Van Hopper are having coffee. The 'girl's' coffee cup then a newspaper are in her right hand between shots without sufficient time or obvious motion to change them.
Errors in geography: George is driving on the left-hand side of the road outside Monte Carlo.
Continuity: The second Mrs. De Winter follows Jasper to the cottage. When she sees Jasper, he is standing up, barking in front of the door. She approaches the door and the dog is now lying to one side.
Errors in geography: Twice during the movie, Maxim leaves Manderley to travel to London, once by train and another by car. On each occasion, he manages to get back before dark. Manderley is in Cornwall, as far from London as you can get, and even with 21st century roads, cars and trains, that feat would be impossible.
Factual errors: Impossible police procedure: immediately after the inquest, the Chief Constable starts a possible murder inquiry, on his own, taking the chief suspect with him.