In the episode "Little Ricky Gets a Dog", both Ricky and Lucy separately try to sneak out of the house without the other knowing. During this scene, when Lucy is putting on her jacket you can hear a woman in the audience say, "She beat him to it."
I won't switch apartments. Understand?
Lucy Ricardo: Yes.
Ricky Ricardo: What did I say?
Lucy Ricardo: "I wun't swish aparments".
The Ricardos are said to live in an apartment at 623 East 68th Street, which in real life would be located in the East River. This is not actually a 'goof' because it was done deliberately to avoid legal issues with an actual address.
In some of the episodes, the guest-star's name(s) are voiced over, by conductor, Wilbur Hatch, in the Opening Credits or Closing Credits.
In reruns of the series, much of the music in the beginning and end of scenes were altered or cut to make way for more commercials. Where possible, many of these musical bridges and cues have been fully restored for the DVD release.