It might just be the catchiest Muppet song of them all, beating out "Rubber Duckie," "It's Not Easy Being Green," "Rainbow Connection" and all the rest.

But until reading this Slate article, I had no idea "Mahna Mahna" came from a softcore porn film.

You know "Mahna Mahna," of course. It's not only in the new "Muppets" movie, but it's been on "Sesame Street," "The Muppet Show," and every Muppet music compilation out there. (There's even a version by the band Cake, which has been set to an excellent "Star Wars" montage on YouTube.)

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The song, however, wasn't written by Jim Henson and crew. It was composed by Piero Umiliani, and first heard in a 1968 Italian film that some consider to be softcore pornography, "Sweden: Heaven and Hell." The song plays over a scene where buxom Swedish ladies head for the sauna. The clip actually doesn't show any nudity -- even in the sauna the women are towel-wrapped -- so you can catch the song's introduction below.

The music was later used for the famous sketch in which two cow-like Muppets (called "Snouths" for "snout" and "mouth") provide backup while Mahna Mahna (voiced by Jim Henson himself) gets overly excited and keeps yelling out his signature line.

The very first Muppet version actually features slightly different performers -- you can follow the whole "Mahna Mahna" timeline at the excellent Muppet Wiki page. I love their completely serious explanation of the song's gist: "Although the back-up singers attempt to bring order back to the number, their effort is ultimately futile."

"Mahna Mahna" gets a great showcase in the new "Muppets" movie, as a rotating cast of celebs pop in to help sing along. And it's starting to make its way back onto kids' radio again, which is a big treat for this parent who grew up in the 1970s. Thanks, you Swedish sauna ladies, for giving us this irresistible earworm.

"Mahna Mahna?" "Rainbow Connection?" Tell us your favorite Muppet songs in the comments.

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