Character mistake: David Niven and his father are playing chess, and to checkmate his father, David Niven makes two moves, which you absolutely can not do - the only time you can move 2 pieces is when you move your castle and the king at the same time (castling), but you can't do that when you are in check.
Wuthering Heights (1939)
1 character mistake
Directed by: William Wyler
Starring: Laurence Olivier, David Niven, Flora Robson, Merle Oberon
Continuity mistake: Cathy and Heathcliff run away from two dogs as they spy on the party and Heathcliff helps her up the wall. In the next shot he is already on the wall and jumps down.
Heathcliff: Why are your eyes always empty? Like Linton's eyes.
Isabella: They're not empty, if you'd only look deeper. Look at me. I'm pretty. I'm a woman and I love you. You're all of life to me. Let me be a single breath of it for you.