Well, then, check out this video, sent to me via a forwarded email message.
This video was made in the Antwerp, Belgium Central (Train) Station on the 23rd of March 2009. With no warning to the passengers passing through the station, at 08:00am a recording of Julie Andrews singing 'Do, Re, Mi' begins to play on the public address system.
As the bemused passengers watch in amazement, some 200 dancers begin to appear from the crowd and station entrances.
They created this amazing stunt with just two rehearsals!