So. Your mission, should you decide to accept it, is to take any musical, past or present (future musicals are not allowed), and find a moment where one of the leads is supposed to sing something and instead opens his/her mouth with a completely wrong song.
For example:
Sweeney has just dispatched the judge. His moment of triumph complete, he closes the razor, looks at the audience, and sings:
Regrets. I've had a few.
But then again, too few to mention...The new song can be from any genre: show tune, rock, opera, country western, whatever will most decidedly NOT work in the moment of the show.
Given the almost boundless amount of arcane knowledge on this board, this should be fun.
"That duck was a sexual toy, and it was on display!" -- an unknown Nashville town leader