Character mistake: During the dancing girl scene, as they are singing the praises of Kane, the girl to the immediate right sings out of time with the rest of the dancers during the line "His favorite son." Even though she forgets to sing the line, she can be heard singing it a bit too late. (00:41:00)
Visible crew/equipment: After the ship's captain delivers the Falcon to Sam Spade's office, he collapses on the leather sofa in the foreground. Just after Spade's secretary says, "Is he ...?", the shadow of someone's head passes over the sofa.
Other mistake: When the invitation to the Hunt Ball is shown on the screen, it says that the ball is on Thursday, March 7, but on the night of the ball when Lena gets the telegram from Johnnie, the date of the telegram is March 8, 1938, which would have been the next day. And March 8, 1938, was actually a Tuesday and March 7, 1938 (the day of the Thursday Ball), was actually a Monday.
Visible crew/equipment: After the moving candle/ghost incident involving Ferdie and Camille, and before Moose Matson's money is discovered, Chuck and the doctor come running in, and they all start yelling and talking, there is a person (probably a crew member) briefly visible in the round window in the door in the background.