It earned six Oscars on its way to stealing hearts worldwide and grossing $440 million, but "La La Land" is perhaps doomed to be remembered for the prize it didn't win.

Director Damien Chazelle and his team hugged as they picked up best picture at February's Academy Awards, but it quickly became clear that the wrong movie had been announced.

As one of the worst mix-ups in Oscars history played out live to the world, the media noted one unusual reaction among a sea of perplexed faces: Ryan Gosling was struggling to control his laughter.

The star's giggles quickly went viral and he has since put it down to delight for the cast and crew of real winner "Moonlight," and relief that the sudden panic wasn't caused by something more serious.

But celebrated choreographer Mandy Moore, who taught Gosling and co-star Emma Stone to dance for the movie, thinks he was just embarrassed.

"Ryan's very like that -- he giggles at awkward moments -- so I think you see him giggling but that's just kind of how he deals with awkward things," she told AFP.

Moore, 41, has four Emmy nominations for reality show "So You Think You Can Dance" and choreographed routines for "Silver Linings Playbook," "American Hustle" and "Joy," but had never attended the Oscars.

She recalls sensing something was odd as presenters Warren Beatty and Faye Dunaway -- who it later transpired were holding the wrong card -- dithered onstage over announcing the winner.

- Breaking hearts -

"I was like, 'This is kind of weird -- or maybe they're being dramatic.' And then, when they said 'La La Land,' of course everyone's like 'Wooooaaaaaah!' Everyone's crazy and everyone starts to stand up," she told AFP.

The penny dropped before she had made it to the front, as she saw stage manager Gary Natoli appear before the crowd at Hollywood's Dolby Digital Theatre.