While college flash mobs vary enormously — students at the College of Charleston held a yoga flash mob — most start with one or two dancers, and a group of quietly bewildered onlookers, who laugh, cheer and pull out their cellphones to record the whole thing, as more dancers arrive. The initial participants are usually good dancers, but those who join in tend to be more awkward, occasionally leaning the wrong way, or flailing their hands a bit behind the beat.
http://www.nytimes.com/2011/10/04/education/04flash.html?_r=1
