Watch this! You can see the thought process of others while this guy is expressing something very energetically in the medium of dance. They're all originally thinking "nutter". Then someone else joins in..."probably another nutter". Then a few more, then more and then everyone wants to be involved. The Tipping Point in one short video.
What are the dynamics at play? Music being the common interest; everyone is already gathered together in a community at a festival. Then sparked by a single guy who goes from being a "nutter" to someone who starts a movement, and a bit of a hero. It's worth a watch.