"Sis boom bah."

For most youngsters, that phrase means nothing. Others of a certain age recognize those words as part of cheer--either on its own or part of a longer cheer called "The Locomotive."

Those of a certain age may also remember "sis boom bah" as the set up to what is former Tonight Show host Johnny Carson's most famous joke.

The date was August 5, 1981. Air traffic controllers were on strike. The Major League Baseball strike had just ended. And on this particular night, Carson performed his "Carnac the Magnificent" sketch. Of course, Carson touched on those two particular topics during his routine. However, it was his allusion to the old college cheer that gained him the loudest and longest laugh of the night.

Here's how it played out on air.

The answer: "Sis boom bah."
The question: "Describe the sound made when a sheep explodes."

The exchange sent Carson, sidekick Ed McMahon, and the entire audience into a fit of hysteria. McMahon's usual canned laugh was absent. In its place, a genuine, hearty belly laugh. The usually buttoned-up Carson needed almost one minute--53 seconds to be precise--to regain his composure. The audience didn't help either of them, as their laughter and applause kept Carson and McMahon rolling.

According to McMahon, Carson warned him that one of the jokes in the "Carnac" bit could bring the show to a halt. Here's how McMahon remembered it.

In 1992, Carson ranked "Sis boom bah" as the second-best moment in his 30-year run as host of the Tonight Show. Only the Ed Ames tomahawk incident ranked higher.

If you'd like to see the full seven-minute Carnac routine from the August 5, 1981, edition of the Tonight Show Starring Johnny Carson, click the window below.

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