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 can be seen on the wall to the right, and 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)Super Grover
Other mistake: Lucy walks out on the balcony and sees Van Johnson sleeping on a lounge chair by the swimming pool. The photographic backdrop shows automobiles, trees, mountains, the Roosevelt hotel and many other buildings of Hollywood but when Lucy goes to the pool and sits on the lounge chair next to Van Johnson, the background is just a plain painted backdrop with no cars, trees, mountains or buildings. This plain backdrop also appears in the episode with Harpo Marx.Steven Lee
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.
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)Super Grover
Continuity mistake: In season 2, "Anniversary Present", Lucy has the 19th circled on the wall calendar, which is the date of their wedding anniversary, but in this episode when the license bureau in Greenwich, Connecticut sends Ricky a telegram with their wedding date, it's now on the 7th.Super Grover
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)Super Grover