Episode #35 "Ricky Asks for a Raise," Lucy, Fred and Ethel do the quick-change act to get Ricky's job back. One of the three is seated at a table supposedly for 12, but there are only 4 places set at the table!
In the episode "Breaking the Lease" #18, Ethel plays such songs as Sweet Sue. In a later episode (#91 "Lucy's Club Dance"), Ethel can definitely not play the piano. In "Ragtime Band" #173, Ethel can't play the piano there as well, and then in the Lucy Desi Comedy Hour with Ernie and Edie Kovacs, Ethel plays the piano accompaniment for Edie's song.
In episode #1, "Lucy Thinks Ricky is Trying to Murder Her", when Lucy and Ricky are dancing, you can see part of the bedroom at the left side of the screen.
In the I LOVE LUCY pilot episode, right before Ricky gets up, a shadow quickly passes by the dresser in front of his bed.
Related Episodes:
In episode #37 "The Handcuffs", the handcuffs come undone but Lucy craftily re-latches them. This happens the first time Ricky goes to the phone and pulls Lucy with him.
In episode #18 "Breaking the Lease," when Fred and Ethel leave after singing "Sweet Sue" in the beginning they each turn a different direction out the door.