Flash mobs, defined by Webster's as "a group of people who organize on the Internet and then quickly assemble in a public place, do something bizarre, and disperse," have become part of global pop culture. The clips below feature some that were organized for advertisements, some for commemoration, and some just for fun -- but all were carefully planned in order to surprise unsuspecting passersby.
Flash mob -- featuring the university's president -- in the student union building at The Ohio State University in Columbus, Ohio in 2010
Pillow fight flash mob in Birmingham, UK in 2007
"The Great Trafalgar Square Freeze" in London, UK in 2008
Flash mob performance choreographed for a Belgian television show, filmed at Central Station in Antwerp, Belgium in 2009
Michael Jackson-themed flash mob in Paris, France in 2009
The Who-themed flash mob in San Francisco, CA in 2009
Flash mob performance choreographed for T-Mobile commercial, filmed at Heathrow Terminal 5 in London, UK in 2010