When Christine is reading a book to Rhoda, you can clearly see the cover and the title "Inside the Castle Wall". Later, when the Rhoda has fallen asleep and Christine closes up the book, you can see a gold (or silver) disk on the cover which wasn't there before.
When Rhoada and Leroy are talking outside, she is working on a puzzle. When Rhoada is facing Leroy the pieces to the puzzle are on the table, when Leroy is facing Rhoda, the pieces are not there. When it goes back to Rhoada, the pieces are again outside the puzzle.
When Christine is reading the book to Rhoda and the shot is behind Rhoda, the covers are down around her waist and she is lying on her side. When the shot is in front or Rhoda, the covers are tucked up under her chin and she is lying more on her back. In the next shot, behind her again, the covers are again around her waist and she's on her side.
When Leroy is telling Rhoda that blood can't be washed off of a stick, in the shot taken facing Rhoda she is leaning on the table with both hands, but as soon it switches to a shot from her right side, she's standing upright with her arms bent.
Shortly before Richard Bravo enters, Mrs. Penmark fixes Mr. Tasker a gin and tonic. Tasker takes the drink with his right hand, but when the shot changes slightly, he's suddenly holding the drink with his left hand and leaning on the cart with his right.
At the end of the arbor scene, as Rhoda's mother is calling her, in the shot taken from inside the arbor the pile of excelsior is almost entirely on the lawn, but in the reverse shot showing it from Christine's perspective through the window, the excelsior is on the dirt or paved area next to the lawn.
When Christine scolds Rhoda for asking for a garnet as well as a turquoise, the reflection of someone, probably Mervyn LeRoy, sitting in a chair with his legs crossed is visible in the coffee pot. Addition: Just to the left of the reflection that is assumed to be LeRoy you can see other crew members moving in the shadow of the door-frame reflected in the coffee pot.
When Christine Penmark and Monica Breedlove fetch the locket, Christine hands it to Monica. When Monica leaves the bedroom a crewman's hand holding a cloth is seen at the bottom left of the bedroom door.
When Leroy goes down to the incinerator after talking to Rhoda. As he opens the incinerator he goes to a lot of trouble not to be burned by the metal doors. But when he gets the doors open. After that, he just reaches right in and grabs the soles of the shoes right out of the apparently hot incinerator.