When Miss Lewis and Lucy are talking, a cymbal is heard. A band member accidentally hit the cymbal. The nightclub filming set was next to the apartment set.
Just before the toast pops out of the toaster, you can see Lucy activate the switch under the table to launch it.
Desi refers to the single Miss Lewis as "Mrs. Lewis."
When the last child with the drum exits the scene he breaks the 4th wall by waving to the audience.