Flash mobs are generally groups of people who gather in one place for a spontaneous performance of sorts.  This movement has its roots in Manhattan.  It was started in 2003 by Harper Magazine’s senior editor, Bill Wasik. Though essentially harmless, flash mobs have caused some disturbance and required police attention.  Basically, they’re supposed to be fun events where a group of people suddenly start dancing as featured in TV shows like Glee, Modern Family and even Oprah. However, there are some places that prohibit flash mobs due to public safety concerns.  The biggest flash mob was a pillow fight flash mob which happened on March 22, 2008 which over 20 cities across the world participated in.