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Strange though it may sound, it’s The Flail’s deep knowledge of and respect for the history of jazz that makes them so unpredictable. You’ll hear the New York quintet open its set with a catchy but lopsidedly rhythmic number—à la Thelonious Monk—and settle in, thinking you know what you’re in for. Then the group will knock you on your ass with a gospel-steeped New Orleans tune, send you reeling with a sprawling free improvisation, and finish you off with a swing-era romp. Yet there’s a core to the collective’s sound, a tense post-bop that manifests itself in uneasy harmonies and themes, and releases with stylistic costume changes. More important, The Flail has a killer pianist. Brian Marsella alone is worth the price of admission, but as it stands, he’s merely the anchor of a group that shows how flexible the standard trumpet-and-tenor quintet can be.

The Flail performs at 8 and 10 p.m. at Blues Alley, 1073 Wisconsin Ave. NW. $20.