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.
Factual error: When Ricky, Fred, and Ethel are rehearsing the hospital run, we can see the area to the left and right of the couch, as well as the back wall by the desk. The problem is the telephone cord doesn't actually lead anywhere, it's just coiled up under the couch and not connected to anything. When Lucy says it's time to go to the hospital, Ethel uses the phone to contact the doctor but gets a busy signal, which would be quite impossible. (00:09:55)Super Grover