Continuity mistake: When the maid comes into the room Helen is clenching her right hand by her side. The camera cuts to face Helen and she is clutching her hands in front of her body. (01:23:05)
Continuity mistake: Holmes throws an object through the window to let the glass and let the poisonous gas out, but the next shot shows Holmes helping Watson to a completely open window.
Continuity mistake: Johnnie, Lina and Beaky are playing anagrams. Lina spells out the word MURDER with an M as the first letter. The shot cuts away and then back again, and now the first letter is an inverted W. (01:01:40)
Continuity mistake: Dr. Luther Brooks is in the changing room with Dr. Dan Wharton. During their conversation, one of the lockers behind Brooks' is open, its door quite close to him. In the close-ups though, all the lockers are closed. The shadows are also different. (00:04:00 - 00:04:40)
Continuity mistake: Dick Powell puts his gun in his left trenchcoat pocket and then 2 minutes later takes the same gun out of his right pocket.
Continuity mistake: The protagonist wakes up screaming and runs away from her cabin. A conductor restrains her. During the scene, the shadows on the wall/poster and on the torso of the black helper heavily change depending on the camera angle used. (00:02:25)
Continuity mistake: When Robert Taylor escapes from the asylum, and is driving the second car he steals, the car is shown at least once with windshield wipers pivoting from above the windshield, then shown with the wipers pivoting from below the windshield. Clearly, these are two different cars. I think the studio borrowed wiper footage from the scene in which he is driving the first stolen car, to use at moments in the scene in which he is driving in the second car.
Continuity mistake: The Cadillac limo changes models at times, also having blackwall or whitewall tires.
Continuity mistake: In the beginning of the movie, as Louise is walking, she has on regular pumps with tassels, but when she crosses the street and is standing in front of a church, she has on open-back pumps. No tassels.