“What the hell is this?” The guy standing next to me asks his friend. His friend shakes his head.

Cocorosie has just begun to play to a packed Paradise Rock Club in Boston.

A woman in a newsboy cap strums a harp and when she opens her mouth, opera warbles out. A tinny prerecorded loop plays the mooing of a child’s toy cow.

A few minutes later, the same guy says, “what is this?” This time, he’s staring at the band, enraptured. Converted. The rest of the crowd—exactly the kind you’d expect to gather on a Saturday night to hear a woman sing opera while her sister plays a series of cat meows—is similarly transfixed; faces have turned like sunflowers toward the stage.

There’s no way Cocorosie could play an average show—there’s nothing remotely average about them.

As a band, Cocorosie defies labels, though their record company, Touch and Go, aptly describes them as “tiny field mice singing gospel.”

Two sisters form the band. Sierra sings opera and plays the harp, guitar, piano, and kazoo. (The fact that the previous sentence is completely devoid of irony or sarcasm indicates the originality that makes Cocorosie so compelling). At the show, Sierra, with smudged eye make-up and exaggerated facial expressions, resembles a weeping clown. As she sings, she sometimes rocks back and forth as though comforting herself. Her unholy voice rises and falls manically, like a ghost haunting the opera.

The other sister, Bianca, has the tinny, trembling voice of a shriveled grandmother (with impressive range, of course). She manipulates various children’s toys, electronics, and other strange noisemakers. She wears a bandanna over hair that splits into two braids and she’s painted a V over the front of her face so that she looks like a cross between Skeletor and Raggedy Ann.

They’ve got a bassist on stage, but he’s practically invisible. A beatboxer supplies percussion, changing up and laying down grooves that ground the soaring voices and echoing loops.

They play only a few of their more upbeat songs—I’m surprised by the absence of favorites such as “Noah’s Ark.” The crowd dances when the beat picks up, but dancing isn’t the goal of the audience or the band. The show primarily consists of songs that make the hair on the back of your neck stand up.

Sierra’s vocals induce shivers, especially when her voice curls in on itself and becomes achingly plaintive. She doubles over and croons, “All I want in my life / is to be your housewife,” pulling at nothing with desperate hands. I keep thinking that the crowd will grow weary of this bizarre slow sadness, but they don’t. Cocorosie creates a mood I’ve never quite seen before at a concert—the sisters have cast a spell like a net over the crowd.

The fairy tale story of Cocorosie’s formation is consistent with their magical aura. Sierra and Bianca were estranged for much of their adolescence; Bianca studied in Brooklyn and Sierra moved to Paris to sing opera. In 2003, Bianca showed up at Sierra’s apartment and the two of them almost immediately began recording La Maison de mon Reve, which they recorded in the acoustical epicenter of the house—the bathroom.

They intended to keep La Maison among friends, but in late 2003 Touch and Go got the album, fell under the spell, and pursued a contract with the sisters.

Cocorosie perform as though they’re curled up in the bathtub in a roomful of friends. I feel communion with the band and with everyone else who has shown up and submitted themselves to Cocorosie’s charms. We all—even the skeptic from the beginning of the show—have fallen for this strange rainbowarrior music and for the band that takes spare parts, vocal gymnastics, and magic to make it so.