Posted just for your general entertainment. It must be quite an experience to suddenly be caught up in one of these.
From Wikipedia:
“A flash mob (or flashmob) is a group of people who assemble suddenly in a public place, perform an unusual and pointless act for a brief time, then disperse.”
Perhaps one for the Singing for Pleasure group:
http://www.youtube.com/watch?v=SXh7JR9oKVE
Mike