Continuity: When the original actor playing Mr. Hughes died in the middle of filming, he was replaced by a double, who completed his scenes with his back mostly to the camera. Apparently, however, nobody noticed that the original actor had significantly darker hair than his replacement. Therefore, Mr. Hughes's hair turns white in several scenes, including the sequence where his wife says goodbye to him in the casino, and his confrontation with the count at the villa.
Continuity: When the Count seats Mrs. Hughes at the roulette table, she is wearing a different gown than the one in the rest of the scene.