You can already hear it in your head, right? MAH NA MAH NA.

Now, a biographer of Muppets creator Jim Henson has traced the origin of the earworm to a viewing of an Italian sexploitation movie in Midtown.

Brian Jay Jones wrote "Jim Henson: The Biography." He said the original song that captured Henson's attention was part of the soundtrack.

"I spoke with Frank Oz, and I said, where did you see it? Where did Jim hear 'Mah Na Mah Na?'" Jones said in an interview. “And he said ‘Oh, oh, oh yeah! Jim and I walked around the corner to go see that movie.’"

“Sweden: Heaven and Hell” promised a lurid tale of sex and drugs from “the sex capital of the world, where topless bands beat out the throbbing rhythms of a turned-on generation.”

Jones said the original song that captured Henson's attention was from that score. It was called "Mah Nà Mah Nà," and was written by the Italian composer Piero Umiliani.

The film, which takes a look at Sweden's supposed culture of promiscuity and drugs, was released in Italy in September 1968.

Jones says by August 1969, it had made its way to a run at the Avco Embassy East theater on East 58th Street. By early October, Henson and Frank Oz — the legendary puppeteer who gave voice to Cookie Monster, Fozzie Bear and Yoda — had popped in to watch it.

Just a few months later in November, the song made its debut on "Sesame Street," crooned by a bedraggled, hairy little Muppet and two other Muppets with little girl dresses, high voices and long hair.

That was followed that same month by the version we all now know, which debuted on "The Ed Sullivan Show."

Jones said he was very impressed by that timeline.

“From the moment he saw it, to the moment he got the puppets built, had the idea in mind, rehearsed it, performed it, got it on TV it was less than three months,” he said.

That version featured a Muppet character named Mahna Mahna, who sings accompanied by two Snowths — hot pink alien creatures with luscious black eyelashes and disconcertingly round mouths.

“What it tells you is that Jim Henson could find inspiration any place,” Jones said of the blue movie inspiration for the children’s classic. “Only Jim Henson would walk out and turn to Frank Oz and say, 'But did you hear the song?'”