CANNES, France (AP) — One of the most memorable lines — and Rob Reiner’s personal favorite — of “This Is Spinal Tap” goes: “There’s a fine line between stupid and clever.”

You could say the same thing about the classic 1984 mockumentary. It could have so easily not panned out. No one in Hollywood thought it was a good idea. It was saved by Norman Lear who, after Reiner made his pitch and departed, is said to have turned to the executives in the room and announced: “Who’s going to tell him he can’t do it?”

Now, Reiner and company want to get the band back together for a sequel. Reiner was at the Cannes Film Festival this week for an anniversary screening on the beach of “This Is Spinal Tap” and to drum up excitement for the just-announced sequel that will also see Michael McKean, Harry Shearer, and Christopher Guest reprise their roles as band members David St. Hubbins, Derek Smalls and Nigel Tufnel.

“The bar is high. There’s no question about it,” Reiner said in an interview by the beach. “And we wrestled with that forever, whether or not we should even bother to do it. But we had an idea. Over the years, people have come up and said, ‘Oh, you should do a sequel.’ We’ve always said, ‘No, no, no.’ But as time went by, we finally had something we think can work. And we’ll find out!”

The 1984 movie had no script, just a four-page outline. It was almost entirely improvised. Reiner’s first cut of the film was seven hours long. Even the jokes they did have planned — like the infamous “these amps goes to 11” scene — were filmed off-the-cuff.

“Quick!” Reiner recalls shouting. “Make an amp with an extra number on it!”

But what teetered so close to never panning out in the first place, has of course become one of the most beloved comedies of the ’80s and a massive influence to countless mockumentaries that have followed. It is even in the Library of Congress.

Reiner assures that this time, too, there will be no screenplay. He will depend on the still sharp improvisational talents of his cast, who have carried on Spinal Tap — a fictional band turned into a semi-real one — in occasional concerts in the intervening decades. Reiner’s character, the director Marti DeBergi (styled after Martin Scorsese in The Band concert documentary “The Last Waltz”), will naturally return.

“Here we are 40 years later and Marti DeBergi — who has not been the greatest filmmaker, let’s put it that way. The man made ‘Kramer vs. Kramer vs. Godzilla.’ And I think he did ‘Attack of the 52-Foot Woman,'” says Reiner. “Because he said there’s going to be this reunion, we wanted to make this film, and we’ve given him free reign.”

When “This Is Spinal Tap” was first released, many thought Spinal Tap was a real band. Reiner, who studied rock documentaries like “The Kids Are Alright” and “The Song Remains the Same” for preparation, enlisted a cinematographer, Peter Smokler, with a documentary background. What was real and what was parody was almost indistinguishable. Sting, Reiner says, has since told him he watched it countless times but didn’t know if he should laugh or cry.

And some bits were taken straight from rock ‘n’ roll lore. The band getting lost on their way to the stage came from an experience by Tom Petty and the Heartbreakers, who may have been enjoying the pre-show backstage atmosphere too much.

Asked if Scorsese ever spoke to him about Reiner’s riff on him, Reiner responds: “Initially, Marty got mad. But over the years, he’s come to love it. We did ‘Wolf of Wall Street’ a few years ago and we talked about it. He said, ‘Ah, I love it. I love that you did that.'”

“The Last Waltz” will again be a major touchstone for the sequel which Reiner is developing for his re-launched production company Castle Rock. Reiner’s plan entails Spinal Tap reconvening for one last show.

Many of Reiner’s most beloved films are seemingly sequel-proof. Recapturing the tone of “The Princess Bride”? Inconceivable. (Writer William Goldman did try, though.) And it’s just as hard to imagine the magic of “Stand by Me” or “When Harry Met Sally” being captured a second time. But “Spinal Tap,” Reiner thinks, isn’t done rocking.

“If you have an idea,” he says, “then you say, ‘OK.'”

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Follow AP Film Writer Jake Coyle on Twitter at: http://twitter.com/jakecoyleAP

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