I’m a little late with this — it took place May 2 — but it’s still worth passing on. The Copenhagen Philharmonic, established in 1843, staged a flash-mob performance of Ravel’s “Bolero” — complete with kettle drums! — in Copenhagen’s Central Station. It’s a well chosen piece of music, because it lets them start with just a few musicians and gradually increase to a full orchestra. It’s fun to watch the reaction of the travelers as they slowly realize what’s happening, their puzzlement and curiosity growing into delight and enthusiasm.