Visible crew/equipment: After Lucy phones Ricky and fibs about a man being on the fire escape, when Ethel and Fred rush in looking for Lucy, two actors' tape marks are visible on the floor where Fred and Ethel stand, beside the couch. (00:06:20)
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.
Audio problem: About 6 minutes in, a friend of Fred comes to the door and Ricky answers it. The man says Mr. Cardo instead of Mr. Ricardo, but Ricky says yes anyway.
Visible crew/equipment: At the very start of the opening shot, when Lucy is at the stove, there's a visible crew member at the right side of the screen.
Continuity mistake: After Fred secures the chain lock to the front door, with the chain mounted onto the frame of the door, Fred then slides the chain into the door's slide-catch to show Lucy the "burglarproof chain." When Ethel opens the door the chain itself is ripped off the frame, leaving the chain (and the piece that was screwed to the frame) dangling from the slide-catch attached to the door, but in Ethel's closeup the chain is still mounted to the door's frame. (00:01:40)
Visible crew/equipment: When Ethel is about to open the door because Fred is too "busy" to do it, the shadow of moving boom equipment is visible on the wall to the right. Then after Ethel opens the door to find Lucy dressed in her starlet outfit, when Lucy walks in disappointed that she was recognized, in the next shot facing Ethel the shadow of the moving boom mic can be seen on the door. (00:10:40)
Visible crew/equipment: After take one of Ricky's Screen Test, when the director says to Lucy, "I thought it might add interest to the scene if you could make it go around and around like a lighthouse!", the Ricardo's kitchen cupboards and fridge are visible off stage to the left of the director's head.
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.
Visible crew/equipment: When Lucy's sitting on the piano looking out the window at their new car, just as Ricky walks into the living room we can see the shadow of the mic equipment moving overhead, likely adjusting to the actor's position. (00:07:10)
Visible crew/equipment: When Ethel's on the stoop in front of the building waiting for Lucy and Ricky, right before Ethel asks Ricky about Lucy's driving lesson, just as Ricky drives up we can see cables moving in front of the new Pontiac pulling the car. Then, when Ethel crashes the new Pontiac into the old car, the jiggling cables are again in front of the new car. Lastly, when Lucy finally starts the old car's engine, now there's a moving cable in front of the old car as well. (00:09:50)
Revealing mistake: Look closely at the Ricardos' new Pontiac convertible. There is no glass within the windshield frame.
California, Here We Come! - S4-E13
Visible crew/equipment: When "Mickey" takes his mother-in-law's suitcases to the back, just as Lucy and her mother sit down on the couch, we can see the bright shadow of something moving across the piano behind them. (00:06:50)
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)
California, Here We Come! - S4-E13
Visible crew/equipment: When they're all finally in the Pontiac ready to leave NYC, just as Ricky starts to drive away we can see cables jiggling under the Pontiac, to the left of the front tire, pulling the car. Funny to see how Ricky puts his hand on the gear stick, but never actually does anything with it. (00:23:40)
First Stop - S4-E14
Continuity mistake: When Ricky stops the car and backs up trying to locate Aunt Sally's, Lucy gets out of the car wearing a coat and a pantsuit underneath, but in the exterior shot she's wearing a skirt set when she walks over to the shed to read the sign. (00:03:50)
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
Visible crew/equipment: While Lucy and Ricky are lying in the sagging mattress "canoe", when the train passes and their bed rolls towards the bunk bed, the end of the set wall is visible at the right side of the screen. (00:17:30)
First Stop - S4-E14
Visible crew/equipment: After driving all day, the Ricardos and Mertzes stop by a run-down diner then end up spending the night in their shared cabin. While they're all in their beds, the vibration of the nearby train causes the Ricardos' bed to shakily slide towards the Mertzes and then back again. The wires attached to the Ricardo's bed are visible, coming from the hole at the bottom of the left wall, and the leg at the foot of the bed is set in a track attached to the floor, which keeps the bed on course.
First Stop - S4-E14
Continuity mistake: In this episode, Fred and Ethel claim that the bed they are sleeping in is just like the one they have been sleeping on for years. It is double bed with a big sag in the middle. However in an earlier episode "Vacation from Marriage" they show Lucy and Ethel in the the Mertz's bedroom and they have twin beds.
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.
