There must be something in the air down there, some sort of compound that frees the imagination. Whatever it is, it allows St. Louis Rep staffers to cut loose and re-explore theater in ways that don't happen on the Mainstage. Right now the Emerson Studio Theatre is just about the only place in town where you can consistently expect the unexpected. This past season saw the Studio functioning at its most creative. Dael Orlandersmith's incendiary Yellowman, the theatrical equivalent of picking at a raw scab, was directed with passionate intensity by Rep associate artistic director Susan Gregg. In stark contrast, Charlotte Jones' Humble Boy delivered an enchanted evening of civility and intelligence. The production, staged by Rep artistic director Steven Woolf, found virtues that were missing in the original New York staging. Not all Studio productions work, but that trek into the belly of the beast known as the Loretto-Hilton Center is always a venture worth risking.