Aileen and the Speedlites

During our Canon EOS Immersion Seminar in Chicago this afternoon, our model Aileen posed on stage while the audience pointed their Speedlites back towards us. I photographed Aileen using a Canon EOS 7D with a Speedlite 580 EX II set to Master and instructed the audience to set their respective Speedlites to Slave. Since there is no limit to how many Speedlites can be assigned to a Group, when I pushed my shutter, ALL of the other Speedlites in the auditorium fired as well...