  Human collective behavior can vary from calm to panicked depending on social
context. Using videos publicly available online, we study the highly energized
collective motion of attendees at heavy metal concerts. We find these extreme
social gatherings generate similarly extreme behaviors: a disordered gas-like
state called a mosh pit and an ordered vortex-like state called a circle pit.
Both phenomena are reproduced in flocking simulations demonstrating that human
collective behavior is consistent with the predictions of simplified models.
