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.
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.
Lucy Misses the Mertzes - S6-E16
Other mistake: When Ricky and Lucy go down to the main floor of their new home to 'inspect' for burglars after hearing a noise, the outside wind is loud and howling, yet the trees outside the bay window do not move, indicating this was shot in a studio.
Visible crew/equipment: The studio 'wallpaper lines' are very visible as Ricky "exits" the screen on horseback.
Continuity mistake: When Lucy, disguised as the Agent, leaves Mr. Reilly's office for the last time, she suddenly reappears on his balcony overlooking the flowers as he gives dictation to his secretary. When she'd have had to venture out of a window from another part of the office elsewhere. Purely a sight gag for the show, no less.
Other mistake: When Lucy responds to the money matter about her hair care, she states, "I can be a thin redhead or a fat brunette," when her real-life natural hair colour was blonde (later dyed to enhance her film career).
Suggested correction: Lucille Ball was naturally blonde. Lucy Ricardo was a brunette. This is, at best, trivia.
Character mistake: After Ethel chooses the ladies who'll play instruments for their own orchestra, Fred enters the Ricardo apartment with muffs over his ears as off-key plucky piano is heard in the background, indicating Ethel is playing very badly, when in all prior episodes she played fluently for any of their show warm-up numbers.
