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.
Deliberate mistake: After Fred and Ethel arrive at Richard Widmark's house dressed as mental hospital staff, when Lucy hugs Ricky and holds out the grapefruit for Widmark to sign, the last closeup of the adorable St. Bernard is a flipped shot - note the chair in the hallway which should be to the left of the table, but is now to the right of the table. (00:25:05)
Continuity mistake: When Ethel asks her old friend Billy to take a group photo of her with Fred and the Ricardos, Ethel poses with everyone as Billy takes only one shot of them together, but when Lucy reads the newspaper article Ethel is posed differently in the cropped "group" picture. (00:12:15 - 00:16:35)
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)
Continuity mistake: When Lucy and Ricky are discussing the dance at the beginning of the episode and she turns away from him after she tells him "that's all there is to it," however in the next shot she is still facing towards him.
Revealing mistake: Lucy, Fred and Ethel are admiring the celebrity footprints in cement outside Grauman's Chinese Theatre in Hollywood. In several scenes, the shadows cast by Lucy, Fred, Ethel and a passerby make it very obvious that what appears to be the ticket office, entrance and front wall are actually just a painted backdrop.
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.
The Adagio - S1-E12
Character mistake: Lucy turns in for the night in full makeup and lipstick, instead of washing up.
Character mistake: When Fred, Ethel, and Ricky confront Lucy on what she wrote about them in her novel Ricky states "I'm so hammy I should go lie down between two slices of rye bread." This is incorrect. Lucy wrote "He turned into such a big ham you could stuff him with cloves."
Continuity mistake: The Mertz' check out of the hotel and are in the garage on a motorcycle. Later they are back in their hotel room with Fred napping in a chair with a hurt shoulder.
Suggested correction: Ethel and Fred checked out of room 317, intending to leave. Later, after their motorcycle crashed, Ethel and Fred checked back in and were given room 372 (time codes 00:09:05 and 00:12:15), so Fred (with his hurt shoulder) is napping in the chair in his and Ethel's new room. There's no continuity mistake.
