It started randomly, as collaborations often do for young people with high-speed connections, limited budgets and big ideas. Back in the summer of 2009, Jacob Krupnick, an aspiring art photographer in his mid-20s, persuaded a fashion P.R. company to hire him to make a promotional video for a footwear show. He went on Craigslist to recruit 50 dancers (“all skills, all ages, all bodies”) to come to a makeshift studio in the Meatpacking District one hot night in July. Payment was in pizza slices.

Anne Marsen was 20 that summer, still recovering from a high-anxiety childhood in Teaneck, N.J.: competitive ballet school, performing in “ The Nutcracker ” at Lincoln Center and the ever-accelerating pressure to be the best and skinniest and en pointe-iest girl in class. Since dropping out of the University of the Arts in Philadelphia a year earlier, she had gone rogue, dance-wise, taking three or four classes a day from studios all over New York City — jazz, modern, tap, salsa, flamenco, belly-dancing, break-­dancing, West African, pole dancing, capoeira — borrowing gestures and movements and boiling them all down into her own unique B-girl bouillabaisse. She showed up at Krupnick’s shoot that night sweaty and a little disheveled, straight out of hip-hop class, wearing sweat pants and a faded Dr. Seuss T-shirt. She handed Krupnick her iPod , cued up to a Daft Punk song about robots yearning to be human, and then offered his camera a five-minute high-intensity freestyle that mixed pops, locks, pirouettes, cartwheels and karate kicks with sensuous hip gyrations and imaginary baton twirls.

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In the months that followed, as Krupnick edited the 50 dancers into one sequence, he found himself returning to Marsen’s routine. “There’s something so dynamic and confident and fluid about her movement,” he said when we talked last month in his apartment in Greenpoint, Brooklyn . “It has nothing in common with the pleasure of watching an amazing ballet dancer. It’s more like watching a chameleon on fast forward. She’s playing with her body movement the way a rapper might play with words.”

Krupnick and Marsen both wanted to collaborate again, to make, as Krupnick put it, “something kind of gigantic.” They just didn’t know what that something might be. Then in mid-November, Girl Talk, the mash-up D.J., released his latest album, “All Day,” a stew of samples lifted from 373 songs and recombined into a chaotic, propulsive mix. As Krupnick listened to the album, it struck him that Girl Talk makes music the way Anne Marsen makes dance. “I started to hyperventilate a little bit, the way you do when you get excited about something that you really want to come true,” he told me. “And then I started calling Anne.”

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A month later, Krupnick and Marsen were on the early-morning Staten Island Ferry , along with two other dancers and Krupnick’s wife, carrying boomboxes and cameras and ducking security guards, shooting guerrilla-style test footage for “Girl Walk//All Day,” which Krupnick describes as “an epic, 71-minute-long dance-music video” in which Marsen will dance her way through the entire Girl Talk album and up the island of Manhattan . By the end of the day’s shoot, they had eight solid minutes, which Krupnick cut together and tossed up on Vimeo as a kind of trailer for the full movie, to see if anyone noticed. The first day, 11 people watched. On Day 2, six did. Then on Jan. 12, Gothamist posted the video, and an hour later it appeared on The Huffington Post home page. By day’s end, more than 17,000 people had seen it. On Jan. 28, Krupnick put up a donation page on Kickstarter, hoping to raise $4,800 from strangers to help him and his collaborators make and distribute the complete video. They gave themselves 45 days to meet their financing goal. It took six. By Valentine’s Day , they raised $12,000, and the trailer had been seen almost 60,000 times.

It is no surprise that people go nuts for the trailer. It is weird and joyous, popping with youth and energy. At first, Marsen looks more like an enthusiastic and slightly dorky amateur than a trained dance pro. She wears regular tennis shoes and worn gray cords and an oversize, multicolored jacket, and at one point she falls off the railing of an escalator. It’s not until a minute or so in, as she twirls and gyrates through the ferry’s upper level, staring down the camera with a sly smile on her face as sleepy commuters pretend not to notice, that you start to suspect that you’re watching something more than a little magical.