Revealing mistake: The "hand" holding the gun rotates 180 degrees while the shooter's point of view does not move. A real hand can't reproduce that motion without moving extremely close to the face.
Revealing mistake: In the process shot (dummy auto front seat, scenery visible in back window) where father and daughter are driving off to see the circus, Eddie G. makes a left turn and the scenery follows; but he forgets to return the steering wheel to center, even though the scenery shows the car has straightened out on the new course. Funny - even titans nod. That car should still be circling somewhere.
Revealing mistake: The 'bee' on the window - immobile in the first shot - is just a dummy with static wings. (01:00:45)
Revealing mistake: The cake Mildred lifts is obviously a solid prop as the "frosting" does not smear her dress when she holds it close to her body.
Revealing mistake: In the cave scene, when Dr. Edelman and Talbot come upon Frankenstein's monster in the mud, there is a skeleton lying beside the monster, which Dr. Edelman identifies as probably Dr. Niemann. The prop is an obvious lab skeleton, as you can very clearly see the circumferential line around the skull cap. Also, if you look closely in several shots, you can make out the hook at the top of the skull where it would hang from a lab stand. (00:24:35)
Revealing mistake: When we see the duckling growing up to being Daffy Duck, the calendar behind him keeps changing months but the position of the days are exactly the same.