Revealing mistake: Dooley Wilson (a singer, drummer, and leader of his own touring band) who played "Sam" in the film, couldn't play the piano. A pianist was playing offstage while he sang the songs. If you look at Dooley's hands whenever he is 'playing' the piano, you can see that he is not playing the proper notes. (00:25:30)
Revealing mistake: The ball Lou Gehrig hits that smashes a window doesn't come off his bat. It comes from behind him.
Revealing mistake: In the scene towards the beginning, when the Chinese mob are talking in the car junk yard, the Chinese guy about to be crushed to death is begging for mercy. While the Chinese mob are talking, when the camera pans to the guy about to be killed, you can clearly see that it's a dummy, then in the next shot it's the real guy again.
Revealing mistake: When Jim and Linda are walking outside after the first night Holiday Inn is open, they are walking through the "snow" but leave no footprints behind them. It is obvious that it is simply a stage floor painted white.
Revealing mistake: In one of the last scenes of the movie when the Younger Generation visits George they drive into the scene in their old jalopy Chevrolet. The only problem is, from the front end shot, anyone can see that the body moldings and lines of the car body don't line up with the hood. Also the gas filler cap is visible, in the same shot, on top of the cowl right under the windshield, revealing they hung the front end of a Chevrolet on the front of a Model "A" Ford Deluxe Phaeton. The only car ever produced with a gas tank filler on the cowl right in front of the windshield - Model "A" Fords. Chevys had too much wood in them during the '20s & '30s. They all ended up being infested with termites. So when this movie was made just 10 or 11 years after they were all produced, no Chevys could be found for filming. Chevy Emblem is visible on the radiator shell, but it's a Ford Model "A". Also the four distinctive vent doors available on Chevys, from the day, are visible instead of the louvers of a Model "A" Ford hood. The Cowl Lamps (Parking Lights) are also Model "A". (01:52:00 - 01:54:10)
Revealing mistake: Inventor Dr.Tobel is shown with his bomb sight. Later in the film we see the same equipment, only this time it is Sherlock Holmes' ultraviolet light apparatus. (00:22:05 - 00:45:30)