Lucy Wants New Furniture - S2-E28
Continuity mistake: At the start of the episode, when Lucy puts the baby in the crib there's only one bumper pad and it's on Lucy and Ricky's side of the crib rails, but in the baby's closeup there's a bumper pad at the rails behind him - which is the opposite side of the crib. (00:00:45)
Other mistake: When Ricky is eating out of the can of baked beans, the top of the label has tape hiding the brand name to prevent it from being seen (it looks like Van Camp's). (00:16:50)
Continuity mistake: While Lucy's taking a tally of who everyone's voting for, the writing on the posterboard changes in Lucy's closeups. (00:14:45)
Lucy Goes to the Hospital - S2-E21
Revealing mistake: 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)
Lucy Becomes A Sculptress - S2-E20
Visible crew/equipment: When Fred steps down from the table hunched over and dressed in his long johns, he walks over to the edge of the couch, and there's an L-shape actor's mark on the floor where he stops and cracks a joke about bowling. Then later, when the art critic tries to lift Lucy's head from the table, more tape marks are visible on the floor. (00:18:15)
Visible crew/equipment: After Ricky and Juanita's song rehearsal, when they both join Fred and Ethel at the side table and talk about doing an afternoon performance, the shadow of the moving overhead boom and mic is visible on the wall and curtain, behind Fred and Ethel. (00:17:50)
Continuity mistake: After everyone comes out of the judge's chambers, the door goes from open to shut repeatedly.
The Operetta - S2-E3
Revealing mistake: Near the end when the repossession men are taking away the costumes and scenery, as they are removing Ricky's pants one of the chorus members can be seen waiting backstage for her cue to enter screaming.
Lucy Wants New Furniture - S2-E28
Deliberate mistake: Lucy and Ethel try and hide the new furniture in the kitchen so Ricky won't find out about it. This in turn forces Lucy to run through the Mertz's apartment to retrieve items from her own kitchen when Ricky wants them. This is supposedly done because the furniture blocks the doorway and is wedged in place thus preventing them from using the door. However it is quite clear that there is a lot of room for the furniture to be pushed into the kitchen and not block the door. They say it is wedged on the sink but there is a lot of room on the other side by the cupboards, along the back wall.
Vacation from Marriage - S2-E6
Other mistake: The camera jostles badly when Lucy steps up on the board to cross the plank.
Other mistake: When Ricky comes home at 3:00 am, the toggle light switch is in the down position. Ricky places his hand over the switch plate and the room goes dark, but the toggle light switch is still in the same down position.
Continuity mistake: Here it's said by the Ricardos that Fred and Ethel have been married for 25 years. Problem is in Season 1's episode "The Girls Want To Go To the Nightclub" the Mertzes both say they've been married for 18 years.
Deliberate mistake: When Lucy makes Little Ricky cry instead of laugh, in the closeup we see the adorable real baby, but when Ricky walks away in the wideshot it's an obvious doll sitting in the crib. (00:01:25)
Continuity mistake: When Ricky sings during the rehearsal, there's a pencil tucked behind his ear with its point facing the back of his head, but after Ricky's song is done and he moves the microphone stand, in the next shot when Lucy walks in the pencil point now faces the opposite way, though Ricky hasn't touched the pencil. (00:19:45)
Answer: There is no reason. It's a just a silly plot device, typical of the era. Women characters were often portrayed as making uninformed assumptions or decisions.
raywest ★