Visible crew/equipment: While Ethel's holding Little Ricky trying to soothe the baby, when it cuts to Fred just as he's walking into the bedroom, the sleeve of a crew member and a bit of camera/equipment can be seen at the right side of the screen. (00:03:30)
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.
Chosen answer: It's not known. She may have moved it to the spare room or it may be in a corner just off camera. There could be any number of reasons, though it probably took up too much room on the studio set, and it was removed, making it easier for the actors to move around.
raywest ★