You may not know the name Improv Everywhere, but you've probably heard about at least one of their fascinating social experiments. Notable past missions include the no-pants subway ride, and their reenactment of a U2 show on a rooftop near Madison Square Garden. The self-described "prank collective" has been all about creating provocative and entertaining site-specific experiences for the past decade, with the goal of "[causing] scenes of chaos and joy in public places". Their latest mission was the eighth "mp3 experiment", in which 3500 strangers downloaded an mp3 file, pressed play simultaneously, and by following the directions on the recording, acted out a mass synchronized ballet of movement and action.