Continuity mistake: At the beginning of the scene where the pilot's wife is attacked in her bedroom by (not) Bela Lugosi, look at the pictures on the wall above the bed. After the attack begins, the pictures are different.
Continuity mistake: When in James Mason's house in South Dakota, Cary Grant writes a message to Eva Marie Saint on a matchbook from which several matches are missing. When Ms. Saint subsequently reads the message the matchbook is full.
Continuity mistake: It is supposed to be night when Joe slips out of the hotel, but a daytime sky is visible.
Continuity mistake: Frederick picks up a bottle of champagne out of the ice bucket and shakes it a little. As he does this the foil and wire are still on top. He turns and aims the bottle at his wife, then tips it back and the foil has vanished as he now just removes the wire and cork.
Continuity mistake: The doctor just killed Mr. Fleming. Cut to Agnes Moorehead playing cards; She is casting no shadow on the desk from the side view, but in the view with the camera in front of her, she is projecting a shadow. (00:11:35)
Continuity mistake: When Richard Hannay jumps from the Sheriff's window into a passing truck it is full of bales of hay. The next time we see him in the truck it is full of sheep and the bales of hay have vanished.