Just ten weeks after performing for a record Montreal International Jazz Festival crowd estimated at 70,000 or more (the festival’s largest since Stevie Wonder in 2009), Angine de Poitrine made their New York debut in the considerably smaller, sold-out 700-capacity room at (le) poisson rouge in Greenwich Village.

In Montreal, the masked Québécois duo had looked out over a sea of tens of thousands filling the Place des Festivals. In New York, fans stood just feet away, close enough to study Khn’s custom double-necked guitar-bass, watch his bare feet move across the pedalboard, and see for themselves how two musicians manage to sound like so many more.

The timing was fortunate for the New York audience. The dates were booked near the beginning of Angine de Poitrine’s extraordinary ascent, around the time a viral KEXP performance turned the already buzzing Quebec act into an international phenomenon. Released in February and recorded at France’s Trans Musicales Festival last December, the video has since amassed nearly 20 million views.

Both (le) poisson rouge dates sold out quickly. In the months that followed, the duo moved on to increasingly large venues and festivals around the world, including this summer’s Newport Jazz Festival. They return to New York in November for three nights at the much larger Brooklyn Steel. As several in the crowd noted, the (le) poisson rouge shows may have been their last chance to see the band in a room this small.

Annie-Claude Deschênes, a multidisciplinary Montreal artist who fronts Duchess Says and PyPy in addition to her solo work, opened the night with an electronic/post-punk set that mixed absurdity with performance art. She played with the cameras, moved through the crowd and repeatedly pulled the audience into the performance. At one point, she brought two people onstage to sit at a small table and eat an assortment of Jell-O. Later, she sprayed whipped cream into people’s mouths and jumped off the stage to wade through the crowd.

Deschênes left the room in exactly the right frame of mind for what came next: amused, unsettled and ready for something stranger. Khn and Klek (the drummer) took the stage in their now-familiar black-and-white polka-dot costumes and enormous papier- mâché heads, looking less like members of a rock band than characters who had escaped from a particularly unsettling children’s television show.

Then they started playing. What followed was an eight-song, 75-minute set whose absurd presentation could almost distract from how technically difficult the music is.

Khn handles both guitar and bass on a custom double-necked microtonal instrument, recording short phrases into loopers and layering them in real time while Klek works through constantly shifting rhythmic patterns. Khn operates his pedalboard barefoot, moving between strings and pedals as the parts build –- a bass line, a guitar riff, another layer on top of that. At times, it’s hard to believe all that sound is coming from only two people.

When Khn broke a string, the interruption became one of the funniest moments of the night. Still fully in character, he communicated with his guitar tech without speaking, relying instead on gestures and the strange vocabulary of noises that he and Klek use in place of ordinary stage banter. While the string was being replaced, they turned the delay into a brief jam. The crowd laughed along with them. It didn’t break the spell so much as offer a brief reminder that, yes, there are actually human beings inside those giant heads.

There is almost no traditional conversation with the crowd. Khn and Klek communicate through sounds, exaggerated movements and their signature triangle hand gesture, which was immediately returned by a room already familiar with the ritual. The anonymity, oversized heads and invented language should create distance between performers and audience. Somehow, they have the opposite effect.

That was apparent even before the show. There is no photo pit at (le) poisson rouge, but the photographers were allowed into the room first, which meant we up front. When I told the woman behind me that I would give her my spot after I finished shooting, her eyes filled with tears. It was a small moment, but it said something about the intensity of the band’s following.

While in line outside the venue, fans talked about Angine de Poitrine with a devotion that seemed almost disproportionate to the band’s relatively short history. There were certainly people in the room who had come out of curiosity, wanting to see for themselves what the buzz was about. Judging by the reaction at the end of the night, at least some of that curiosity had turned into fandom.

The music itself may be the most unlikely part of the band’s sudden success. Angine de Poitrine describe what they do as a “Mantra-Rock Dada Pythago-Cubist Orchestra,” which sounds ridiculous but is also not entirely inaccurate. The music draws from math rock, progressive rock, jazz and experimental music, with odd meters and microtonal intervals — pitches that fall between the notes used in conventional Western tuning. Khn’s instrument has additional frets that allow him to play these pitches. To ears accustomed to the familiar intervals of Western pop and rock, the result can feel slightly off kilter. Melodies bend in directions you don’t expect, while the rhythms keep shifting underneath.

And yet, for music this technically demanding and structurally strange, it is remarkably physical. You don’t need to understand microtonality or count changing time signatures. You just feel it.

That may help explain why something this weird has connected with so many people so quickly. Much of contemporary pop is built around familiarity, polish and confessional songwriting. Angine de Poitrine offers almost the inverse: instrumental music with no easily decipherable narrative, deliberately abrasive intervals, complicated rhythms, anonymous musicians and enormous papier-mâché noses. And people are lining up for it.

Their rise may be less an inexplicable viral fluke than evidence that audiences were ready to be surprised. Angine de Poitrine are funny without treating the music as a joke, technically formidable without turning the show into a display of virtuosity, and deeply strange without seeming self-conscious about it. Beneath all the polka dots, triangles and oversized noses are two musicians making extraordinarily complicated music, and somehow making it feel like a party.

For two nights, before they move on to the bigger rooms already waiting for them, a few hundred people got to watch it happen from just a few feet away.

Setlist: Angor, Yor Zarad, Tamebsz, Mata Zyklek, Ababa Hotel, Sarniezz, Fabienk, Sherpa.