Factual error: In the film Lucy and the others make, there is a long sequence of footage played forwards, then "mistakenly" repeated backwards. With the equipment and techniques they were using, this would have required not only making a complete copy of the segment, but also reversing the order of individual frames. Just feeding the film in backwards would have also flipped the image vertically. The result seen would be nearly impossible to produce accidentally.
Continuity mistake: After Lucy tells Mr. Merriweather that he's invited to the seance, when it cuts to Lucy unfolding the card table legs, note the couch behind her with one normal seat cushion on the left, but in the next wideshot there's an additional shorter cushion under the normal cushion. The small towel also repositions itself neatly on the couch. (00:11:55)
Ricky Ricardo: Fred, how often is Ethel's checking account overdrawn?
Fred Mertz: Never.
Ricky Ricardo: Never? How do you manage that?
Ethel Mertz: It's easy. I never had enough money at one time to open a checking account.
Fred Mertz: She spends money like I'm printing it in the basement.