Revealing mistake: When Lucy is cutting up the fake fur coat to scare Ricky, it is clear that the parts that she has to remove are already cut and just loosely sewn in place.
Lucy Is Jealous of Girl Singer - S1-E11
Revealing mistake: During the rehearsal for the Jezebel number, the dancer's skirt trim is already partially torn or unattached to make it easier to tear, and it is clear that Ricky purposely steps on the trim to rip it off the skirt.
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. The rearranging of furniture between episodes occurs often, and would only be a problem if it happens within a scene. From the very start of this episode, the card table is already 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.
Revealing mistake: When Fred and Ethel come with parts of their apartment's ceiling on them look closely at Ethel. The piece on her left shoulder falls off revealing what looks like a velcro pad to keep it in place.
Revealing mistake: When Lucy's pinned against the sink by her bread Ethel goes for a saw. If you watch the doorway you can see her shadow where she's being given the saw.
Revealing mistake: When Ricky brings home the psychiatrist, in all the long shots of the living room from the time Ethel walks around the coffee table toward Fred, we can see that all four coffee table legs have been propped up on stone blocks.
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.
Redecorating - S2-E8
Revealing mistake: At the end of the episode, when Ricky and Lucy walk into the bedroom to see the new wallpaper, look behind them when the bedroom door opens and you'll catch a glimpse of William Frawley - waiting for his cue - hiding behind a wall in the background before he ducks back out of sight.
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 Wants New Furniture - S2-E28
Revealing mistake: When Ricky startles Lucy in the kitchen just as she's getting the salt, she climbs up through the kitchen/living room window, and in the shot from the living room when she and Ricky step down onto the chair, we can see the four long metal brackets which bolt the chair to the floor for safety. (00:13:15)
Revealing mistake: After Ricky and Lucy split up to go fishing Ricky yells that she should watch out for bears, and when Lucy stops at a tree and crouches down, the huge tree beside her jiggles when she leans on it. (00:13:40)
Equal Rights - S3-E3
Revealing mistake: When Lucy and Ethel go down to the jail house to see Rickey and Fred, there is a scene where Lucy says "I wonder how he (Rickey) kisses" and then she kisses him, then Ethel says the same thing about Fred and leans in for a kiss. Problem is she obviously doesn't get anywhere near his lips to touch them for a kiss, yet makes the kissing sound, turns around and says "hmmm" as if the "kiss" wasn't all that . Of course we all know those two characters did not get along on set anyways .
Revealing mistake: When everyone is examining the car that Fred bought, during a shot showing the front of the car, everyone's shadows are falling on the "street" behind the car, making it obvious that it's a painted backdrop.
Revealing mistake: Look closely at the Ricardos' new Pontiac convertible. There is no glass within the windshield frame.
California, Here We Come! - S4-E13
Revealing mistake: The Pontiac's glass windshield is gone when the car is loaded down with everyone's stuff, thanks to Fred's packing, and the windshield is also very noticeably gone when they all finally drive off. The rearview mirror, which should be attached to the windshield frame, is gone as well. (00:20:30 - 00:22:50)
First Stop - S4-E14
Revealing mistake: After the cheese sandwich experience at Skinner's diner, when Lucy takes the wheel and they all drive off heading to Cincinnati, the Pontiac's glass windshield and rearview mirror are gone, and they're gone again when they end up back at that diner the second time. (00:09:20 - 00:10:35)
First Stop - S4-E14
Revealing mistake: When the bed Lucy and Ricky are in moves as a train goes by look real close and you can see the wheels on it to help move it across the set piece.
Suggested correction: Not necessarily an error. My bed frame is on wheels.
Revealing mistake: At the Brown Derby, when Lucy bumps into the waiter causing him to trip and spill the tray all over William Holden, we can see that the waiter's hand is taped to the bottom of the tray for the stunt to be done efficiently. (00:15:15)
Revealing mistake: At the end of Lucy and Van Johnson's dance, Ricky and everyone else clap as Lucy walks through the curtain to head "backstage', and in the next shot just as Lucy walks through the curtain we catch a glimpse of Desi Arnaz standing there waiting for his cue. Then in a few moments Ricky, Ethel, Fred, and Caroline all rush in excitedly to congratulate Lucy. (00:24:55)
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.