Inside the famous theme song

They were the two notes of terror heard around the world.

They were the two notes of terror heard around the world.

But director Steven Spielberg initially laughed off composer John Williams’ “Jaws” theme that would become the signature sound — and sign — of the great white shark’s attack in the summer blockbuster that opened 50 years ago on June 20, 1975.

“I expected to hear something kind of weird and melodic, something tonal, but eerie; something of another world, almost like outer space under the water,” said Spielberg in a 2012 Blu-ray featurette on the making of “Jaws.”

“And what he played me instead, with two fingers on the lower keys, was ‘dun-dun, dun-dun, dun-dun.’ And at first, I began to laugh. He had a great sense of humor, and I thought he was putting me on.”

But Williams was scaring up the menacing motif that would sink its teeth into moviegoers — and terrify beachgoers — for generations to come in the film classic that would launch his and Spielberg’s careers into historic heights.

While Spielberg might have first thought it was a joke, Williams was dead serious about the ominous ostinato of notes E and F played by tuba player Tommy Johnson.

“He said, ‘You can’t be serious?’” Williams — who had previously worked with Spielberg on 1974’s “The Sugarland Express” — told Classic FM in 2022 about his chilling riff to “represent our primordial fear.”

“I think in Spielberg’s mind … you want something really complicated and layered and, you know, atonal horror music or whatever,” film music historian Tim Greiving — who wrote the upcoming biography “John Williams: A Composer’s Life” — exclusively told The Post.

“But John Williams has such a great story instinct that he knew that the simpler, the better, that kind of economy and just, like, pure drive was what this movie needed. So, yeah, in this way he knew better than Spielberg.”

To Greiving, Williams struck just the right note with the “Jaws” theme.

“It so perfectly represents the mindless, just predatory instinct of a shark,” he said. “You can almost think of it as, like, it is the shark.”

But, he added, there’s also a “sense of a heartbeat” that captures ”you in the water with your heart rate kind of accelerating as the shark gets closer to you.”

The “deceptively simple” phrase was just the right hook to harpoon the masses. “It’s just a very effective storytelling device,” said Greiving. “I think anything more complicated than that wouldn’t have been nearly as effective.”

The “Jaws” theme became a cultural touchstone in and of itself.

“Because ‘Jaws’ was such a huge phenomenon, it … just permeated everything,” said Greiving. “And you had this musical signature, this musical brand to that phenomenon. So it’s just an easy way to sort of shorthand reference ‘Jaws’ as a whole phenomenon.”

“I think it’s like the opening of Beethoven’s Fifth or the strings of ‘Psycho.’ It’s just something so instantly recognizable that those kinds of things just catch on … and, you know, they just never go away, right? That’s the brilliance of it.”

However, Greiving notes that the two-note “Jaws” theme that that has struck fear across generations is just a small part of the score that won Williams the first of his four Oscars for Best Original Score.

“I talked to [Oscar-winning composer] Hans Zimmer for my book, and he just said, ‘You know, everyone’s scared of those two notes, but for composers, we’re scared of everything after those two notes, because the whole thing is so impressive,’ ” he said. “And I think John Williams, as he often does, takes a simple idea, a simple motif, and just expands it and develops it into basically a symphony.”

Williams went on to score more than 100 films, including other classic Spielberg collaborations such as “Close Encounters of the Third Kind,” “E.T.: The Extra-Terrestrial,” “Jurassic Park,“ “Schindler’s List” and the “Indiana Jones” franchise,” but he never imagined that the repeated pattern of “Jaws” would never go away.

“At that time, I had no idea that it would have that kind of impact on people,” he told Classic FM.

And Spielberg has credited the “Jaws” theme as a major part of the movie’s success.

“When everyone came out and said ‘Jaws’ scared them out of the water, it was Johnny who scared them out of the water,” Spielberg said in the Blu-ray featurette. “His music was scarier than seeing the shark.”

But for Greiving — whose Williams biography will be released on Sept. 2 — the “Jaws” theme is even bigger than movies.

“I think the two-note theme in ‘Jaws’ is maybe the most famous musical unit in the history of music. I think you could argue that,” he said.

“I think more people around the world recognize these two notes played as the ‘Jaws’ theme more than almost any other piece of music.”