As you know, director Ron Howard got his start as an actor by playing Opie on The Andy Griffith Show. But around the same time, though some people forget, he also made a renowned feature film, starring as Winthrop Paroo in the movie version of The Music Man.
Not long ago, he was on the Conan show, and the conversation moved around to his early career. And in part because The Music Man filmed in the same studio on the Warner Bros. lot where Conan is done (and is mentioned on a plaque), and in part because Conan has often said that The Music Man is is favorite musical (for which he shows fine taste, since it's the first stage musical I ever saw and is one of my two favorites), Conan brought up the movie in conversation.
And quite unexpectedly, after the conversation seemed to be about to move on, without even any prompting, Ron Howard broke into one of his songs! And in character, no less. Conan is clearly about to say something, but to his credit, he immediately stops, likely thinking to himself, "Shut up, guy, let him sing!!"
(Interestingly, in all the years I've seen Ron Howard interviewed, I don't recall him ever being asked about The Music Man. It probably helps that it's Conan's favorite musical, which may have prompted him.)
.And equally fun, Conan himself later gets into the action and performs a song from the musical, as well. (It's worth noting that when he was a writer on The Simpsons, O'Brien famously wrote a popular episode that is loosely inspired by The Music Man, called "Maggie vs. the Monorail.") Oddly, he seems to get so excited talking about all this that he fumbles the name of the main character, referring to him as "Howard Hill." Obviously, he knows better.