Tap dancing often seems intrinsically retrospective, concerned with re-creating the long vanished (and largely unmourned) era of minstrelsy. Plus the form makes dance a competitive sport, a war between athleticism and elegance. For those like Fred Astaire, feet are the hardworking but discreet servants of the patrician body, while for others the feet seem to call the shots, directing the body's motions as thoroughly as the Red Shoes. Both approaches are enjoyable, but either can pall. Just when you're ready to dismiss percussive dance as a quaint sport like curling, however, along comes Sheketak, making their North American debut here. Their completely contemporary approach is concerned neither with athleticism nor with elegance but with communication. The closest analogue to this Israeli troupe of three dancers who make music and two musicians who dance is Blue Man Group: Sheketak's mix of acrobatics, dance, mugging, mime, music, and body pounding produces the same sense of anarchy--and the same exhilaration. Whether banging on stew pots, imitating the moves of the mechanical man who shares their stage, or clapping one another's hands and playing the drums on one another's heads, these dancing Marx Brothers reinvent the art of tap. This weekend they'll appear at Northwestern with the very best traditional practitioners of the form, including Tony winner Savion Glover (August 10 and 11 only). The "Juba: Masters of Tap and Percussive Dance" concerts also feature, in various combinations, the North Carolina Youth Tap Ensemble; Dianne "Lady Di" Walker; American Tap Dance Orchestra soloists Barbara Duffy, Tony Waag, and Margaret Morrison; Ted Levy; Sam Weber; and, from Chicago, Lane Alexander, MADD Rhythms (Bril Barrett and Martin "Tre" Dumas), Jimmy Payne Jr. and Perfect Timing, Idella Reed, Rhythm I.S.S., and Billy Siegenfeld's Jump Rhythm Jazz Project. Northwestern University, Josephine Louis Theatre, 1979 South Campus Dr., Evanston, 847-491-7282. Through August 12: Friday-Saturday, 8 PM; Sunday, 4 PM. $25-$35. Note: The festival's concluding event is a performance of Morton Gould's Tap Dance Concerto by Alexander and the Chicago Sinfonietta September 9 at Dominican University and September 10 at Symphony Center, 312-236-3681. $25-$45.