Hollywood actor Kevin Spacey, who is spending part of his time these days as the artistic director of London’s Old Vic, is instituting a series of recorded messages before performances instructing audiences to turn off their phones, stop crinkling candy wrappers, and just generally sit still and keep quiet. Such admonitions have become common in the U.S., but some in London’s theatre world have a longer memory: “The behaviour of modern audiences is dramatically better than in previous centuries, when armed guards were frequently posted to stop the mob in the pit from storming the stage, and performers were sometimes knocked out by objects thrown from the gallery.”