A moto-perpetuo ostinato in the cello begins Jérôme Ducros’s piece titled for this practice for cello and piano. In 1786, Emperor Joseph II banned this practice at performances of The Marriage of Figaro. Arturo Toscanini was challenged to a duel after refusing to allow this practice at a performance and officially banned it at La Scala in 1921. Emanuel Ax pioneered pairing slow movements of cello sonatas for this practice alongside Brahms’s second piano concerto. Michiura Oshima’s Memories and Mason Bates’s Ford’s Farm are among 27 pieces commissioned for this practice and recorded in an album by Hilary Hahn. A greeting is traditionally shouted before the second (10[1])of three pieces used for this practice at the Vienna New Year’s Concert, which is always Johann Strauss’s waltz The Blue Danube. For 10 points, name this practice in which a piece is played unannounced after the printed program. ■END■