Continuity mistake: During the middle of the film, a butler comes in and out of the Dictator's office several times repeatedly. The door is open and shows the corridor outside the office, casting the shadow of a window off-screen. The shadow changes from small to big bewteen shots.
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.
Continuity mistake: There is a scene when they are all in the press room when he's inside the desk. As Hildy goes to get water you can see she's wearing the black heels she's been wearing throughout the movie. In the next shot as she walks behind the table, if you look through the table legs you can see she's wearing a pair of flat white slippers/loafers.
Continuity mistake: Near the beginning Harriet Vane produces tokens for herself & Lord Peter Wimsey of miniature handcuffs with one cuff "open to symbolise we're giving up on crime". She puts hers on as a bracelet. Immediately after & several times throughout the film it's clear hers is a set of closed handcuffs.
Continuity mistake: As he is talking, Jimmy Stewart is writing on small boxes and placing them in a pile. He sets one down, and when the camera changes, he's suddenly got one in his hand again. (00:27:35)
Other mistake: Noah, the brother, just disappears from the movie with no explanation at all.
Factual error: The movie "Santa Fe Trail" (1940) starring Errol Flynn, Ronald Reagan and Raymond Massey, is the story of John Brown's raid on Harper's Ferry in 1859. The president is shown to be Abraham Lincoln, who wasn't inaugurated until February of 1861.
Other mistake: It's the Professor's 60th birthday and the candles on his cake must be the trick type - they keep going out as the cake is carried into the room, but they quickly come back on again. But when it comes time for the Professor to blow them out, there's no problem - he blows them out easily.