Singer Bobby McFerrin and pianist Chick Corea strolled out together at the start of Saturday's show at Wolf Trap. McFerrin sat on a stool and improvised a rapid-fire series of scat vocal arpeggios; Corea sat down at the grand piano, knocked out a drumbeat with his knuckles on the piano top, then played McFerrin's ad-libs back to him and finally improvised variations on those phrases. When McFerrin began slapping his chest percussively and adding hiccups to his nonstop vocal lines, Corea stood up and plucked the strings inside the piano. Later in the same half-hour piece, McFerrin took over at the piano while Corea sang the scat syllables; still later the two roamed the stage singing a gibberish duet into the same microphone, a duet that turned into mime-dance between two clumsy jugglers.

On and on it went for two hours that were as much improv theater as a musical concert. McFerrin and Corea were the only two people on stage all night, and for the most part, they made it up as they went along. In sharp contrast to most touring concerts, this was a one-of-a-kind, spontaneously improvised event. At times the music lacked much shape or momentum, but there was more than enough compensation in watching these two talents playfully explore the possibilities of sound. Even when they did the old standard "Autumn Leaves," they subjected it to far-afield digressions and show biz parodies. The evening's highlight was "Echoes," a five-part suite recently written by McFerrin and Corea as a duet for piano and vocal sound effects.

The show was recorded for a possible live album, but no audio tape could capture the evening's most inspired moment. McFerrin was pacing the stage, searching for something new to play with, when he spotted a large vase of flowers. He handed the vase to some people in the front row and asked them to pass it back up the rows. When they obliged, McFerrin passed them a glass of water, then his stool and then a stepladder, which the crowd passed hand over hand up the rows. Finally McFerrin threw himself into the audience like a swimmer with outstretched arms, and he was carried by wave after wave of arms, up to the back of the theater and into the night.