Unless you're a performer (or a friend of one), you generally attend open mics out of rock-bottom boredom or morbid fascination, or by mistake. On Monday nights, the Venice Cafe opens its bric-a-brac-crammed space to the usual suspects -- sheepish singer/songwriters, blues burnouts and militant doggerelists. But at this open mic -- one of the best, if not the best, in town -- you never know when a revelation will hit. St. Louis native Kelly Reinert, an off-and-on regular at the Venice free-for-alls, is one such revelation. She's got a hell of a voice: aggressive and sweet, with a kind of working-class sensuality -- none of the fey babydoll quality too common with singerstrummers these days -- that recalls Alice Spencer or even Rory Block. She's not a country singer, but her tone echoes with Midwestern twang; she's not a blues singer, but she can bend and break notes with wild abandon; she's not a jazz singer, but she's technically gifted -- though she never studied -- and she knows the elusive art of wringing emotion from the most musical of moments. She doesn't sing spirituals, but she's as close to a white gospel singer as you'll hear in the bars around town. Her songwriting, on the voice-and-guitar-only debut Rhythm of the Rattlesnake, is as open-hearted and vigorously honest as her delivery. No major statements here: just a recognition of love -- of the body and the soul -- as a source of life and music, and sometimes her unpretentious lyrics attain a Zenlike beauty: "A wise man told me to listen to ripples crash on stones." At the Venice, host Ranger Dave backs her simple chord changes with a flurry of blues and bluegrass riffs, and the distracted, tipsy crowd shuts up and listens. Reinert celebrates her CD release in Maplewood this weekend -- another chance to hear one the best-kept secrets in town.