Continuity mistake: If you look carefully at the monster (Frankenstein) you will see that his face is different in the ending scenes. The reason is, during the movie you see the monster take the woman doctor and throw her out the laboratory window. You then see the monster kind of stumble, which he really did and broke his ankle. So in the final scenes they replaced Lon Chaney Jr. as wolfman with a stuntman, and Lon Chaney Jr. finished the movie as the monster.
Continuity mistake: In the scene where Judy Garland and Fred Astaire go to the nightclub to see Ann Miller, Ann invites Fred to come up and dance with her. When she is dancing by herself, she is wearing red high heels. When Fred comes up, she is wearing red flats.
Audio problem: In a scene when the Blandings first move into their dream house, Cary Grant (Jim Blandings) says something to a workman and his lips clearly don't match what is heard.
Plot hole: When Ralls runs the Witch onto the reef, he is at the helm. As she strikes bow on, the wheel spins madly for no reason, as the tiller ropes would not have been affected by the collision.
Revealing mistake: When Mr. Peabody is fishing, it is obvious that he is in a boat on the floor of a studio. Rear-screen projection is used to show the ocean behind him, but while he is standing in the boat and trying to reel in his catch, the boat is absolutely motionless.