"It's like were doing a show, but in a sense, it's almost like an imaginary holiday," Koster says. "You know that tradition 'mumming'? With Mummers? Well, it's a lot of different incarnations, but in Newfoundland, the mummers cover themselves completely in crazy disguises and go to people's houses in the village. If a mummer comes to your door, you have to give them food, and alcohol, and anything they want, until you can guess who they are."

Those kind of traditions—myths that become practices—fascinate Koster. "There's all these different and funny, little traditions and customs around the world that people use to tap into the magic that's inside of us, and that's always fascinated me," he says. "All these things create other realities, they're actually happening.  It's a reality that's partially composed of the imaginary and partially composed of the real, but once you've invested in it and spent time in it, what's real and what's imagined blur, and it becomes a real, valid reality that you can live inside.  The Music Tapes are very interested in creating other realities."

And how do The Music Tapes achieve this?  By playing house shows, of course.  "It's as simple as there you are, with other people for an evening in another reality that you created together, and that's what we're doing as human beings," says Koster.  "And for us, we're just singing a song."

The Music Tapes perform tomorrow at a house in Arlington. 9:30 p.m.

The bike under the tree: As a devout fan of The Muppets, the guest-Sleigher finds some pleasure in hearing a version "Silent Night" that sounds as if it is being sung by Beaker.

The lump of coal: With its unsteadily oscillating tones the singing saw might rival the slide-whistle for the title of "Most Depressing Instrument Ever." It is difficult for the guest-Sleigher to listen to Koster's interpretation of "Oh Come All Ye Faithful" without being plagued by visions of sad clown-hobos shivering in a rail yard alongside a starving dog and a dwindling campfire.

Cheer factor: Zero. Negatory. Practically non-existent. Still, as far as non-traditional Christmas music goes, the ethereal and downright bizarro sounds that Koster elicits from the saw make a preferable alternative to whatever Mannheim Steamroller is up to this year.