Is there a mic more open than that of the Poets' Groove at the Blue Nile? With a 10:00 p.m. signup on Tuesdays, the night is more casual than the Southern Theater's Balls Cabaret on Saturdays (which requires prior arrangement by phone), and the spectacle is as unpredictable. For three years, spoken-word artist Desdamona has hosted the 18+ open-mic night with a house band featuring Kevin Washington on drums, Alicia Wiley on keys, and other jazz musicians, which might lead you to expect a vibe that skews bohemian and hip-hop. But the band backs anyone who asks, and the crowd has seen it all—the guy who plays Jimi Hendrix covers with Prince lyrics, the poet who stands on his head, the R-rated comedians and earnest country singers who hold nothing back. Last year, when the Blue Nile experienced a blackout during a storm, a group of rappers, vocalists, and other audience members formed a circle in the darkness, improvising for the better part of an hour on the floor. That's as open as it gets.