Comedy collective Improv Everywhere has helped hurl flash mobs into mainstream consciousness, providing urban passersby with some of the most puzzling organized public chaos ever staged. Luckily, the pranks are always heavily documented by IE's creator, Charlie Todd, and the group's latest effort -- the fifth annual MP3 experiment -- proves no less.

In San Francisco, Toronto, New York and Chicago, large groups of people all listened -- in sync -- to the same mp3, in which Steve, the "omnipotent narrator" provides instructions to each listener. Of course, all the directions are essentially exercises in silliness -- involving balloons, stretching and one giant nap -- which, of course, results in a wildly colorful free party.