Audio problem: During various shots in the Ricardo living room one can plainly hear what appears to be the whirring of the camera.
First Stop - S4-E14
Other mistake: When the Ricardos and Mertzes arrive the first time at One Oak Cabins and Cafe the full moon is amid the tops of the trees. When they arrive the second time the full moon is in exactly the same location amid the tree tops as the first time they arrived. Fortunately, hours later when they make their sneaky escape from the cabin and return to their car the moon is no longer in view.
Return Home From Europe - S5-E26
Continuity mistake: As Lucy gets up from her airplane seat holding the big hunk of cheese wrapped in a blanket she is masking as a baby, it bends in half as if it were already cut. This is the scene before she sneaks off to the kitchen to cut it apart. In prior scenes, the cheese is intact and solid. (00:17:10)
The Ricardos Dedicate a Statue - S6-E26
Continuity mistake: When Fred the dog runs onto the couch with Ricky's speech he goes to the right side of the couch and puts his head under a pillow. The shot changes and he is now on the other side of the couch.
Lucy Meets Orson Welles - S6-E3
Continuity mistake: When Ricky comes home and and Lucy tells him she meet Orson Welles, Ricky shuts the door. Later on in the scene the door is suddenly open.
Lucy Meets Orson Welles - S6-E3
Continuity mistake: When Ricky says "From the look in your eyes back to Cuba" Ricky's briefcase suddenly appears on the piano.
Continuity mistake: After the song "Nobody loves the ump" the tiles that are stuck to Lucy's shoes disappear.
Lucy Gets a Paris Gown - S5-E20
Continuity mistake: When Lucy and Ethel are sitting at the table at the cafe just before Ricky and Fred show up, Lucy starts to put her arms on the table. The shot changes and her arms are already on the table.
Continuity mistake: When Lucy is talking about finding an undiscovered artist she is holding a French dictionary. The way she is holding the dictionary changes a couple of times.
Continuity mistake: When Ricky comes over to Lucy, Fred, and Ethel after he sings for the first time, his hands are by his sides. The shot changes his hand are now in his pockets.
The Million Dollar Idea - S3-E12
Continuity mistake: When Ethel says "He's never forgiven Ford for scooping him with the horseless carriage" Lucy is laughing. The shot changes, she is no longer laughing.
Ricky's Old Girlfriend - S3-E11
Visible crew/equipment: In Lucy's dream, when Carlota Romero and Lucy are dancing, the camera pulls out too far and where the set carpet ends and the studio floor begins can be seen.
Plot hole: A block of cement that big would be very heavy, far too heavy for Lucy and Ethel to carry, not to mention someone would have noticed them carrying back to their hotel room.
Plot hole: Both couples have the same group of friends and they were all invited to both going away parties planned on the same night at the same location. Isn't it likely that at least one of the main characters would have found out about the other party? But at the end, all seem surprised about the other party that was planned for them.
Continuity mistake: During the scene set in the boat there is no land seen, but in the shots outside the boat, the land is present. In the same scene Ricky is wearing a wide-collared shirt but in the location part, he is shown wearing a white T-shirt.
Plot hole: Despite the plot, Lucy couldn't be fooled by Jimmy and Timmy Hudson. True, they could be fraternal twins but not even Lucy could mistake them for being identical as one's got a higher voice and the other's shorter.
Plot hole: Lucy mentions if Ricky comes home by bus, cab, or subway then they win the bet. Problem is unless they live next to a subway she wouldn't know if he'd used it.
Plot hole: How does Lucy get back up to the apartment bound and gagged? It would seem impossible to hop up all those steps, possibly take several hours if not all night.
The Million Dollar Idea - S3-E12
Character mistake: When Ricky sits down to calculate by hand how much Lucy and Ethel have spent on supplies to make and sell their salad dressing, he adds $7.21 for the groceries, $1.20 for the jars, and 10 cents for the labels. He says his total is $8.31. He miscalculated; the correct total is $8.51. Ironically, his profit calculation is correct at 3 cents a jar. (00:15:10)
The Benefit - S1-E13
Revealing mistake: There's suddenly an upright piano in the living room where Ricky's desk used to be.
Suggested correction: There's nothing sudden about it. From the start of this episode, the card table is at the center of the living room, with the couch pushed back toward the wall, and the desk is behind the couch (holding telephone, etc), up against the wall where the piano usually is in other episodes. Ethel asks Ricky about the sheet music on the piano, and he explains he's been working on a musical number for the show at the Tropicana. So, for this episode's ongoing musical storyline, the positions of the piano and desk have been switched. This occurs again a few episodes later in Breaking the Lease. The rearranging of furniture between episodes occurs often, and would only be a problem if it happens within a scene.