Other mistake: When Abbott and Costello are bringing the first crate (Dracula) into the house of horrors, Abbott tells Costello twice to help with moving the crate. The first time Abbott says to help pull the crate, which is correct. The second time, Abbott says to help push, even though Costello is still pulling.
Other mistake: During opening scene, two faces of Big Ben show different times. One face shows 8:00 and the other shows 9:00.