in nagoya, japan, at ine of the world's most advanced unmanned factories, robots are singing on the job. as it moves down the production line at t he yamazaki machinery works, a large red transport robot hums, take my hand , i'm a stranger in paradise. nearby , another robot offers a selection. from beethovem. why do these mechanical marvels sing while they work? since the robots move freely throughout the factory, engineers have programmed them to switch on their music when they are in motion, warming the plant's few human workers of their presence.