With a flurry of whistles and a text-message command -- "Go!" -- about 100 people dropped to the ground at Salt Lake City's Gallivan Center, playing dead to make a point about global climate change.
At that moment, 8:17 p.m. Thursday, a 30-foot-square red banner unfurled from the nearby Walker Center parking garage, flashing a message to the thousands gathered to hear reggae legends Toots and the Maytals: "CLIMATE CHANGE KILLS."
The protest was an example of a "flash mob," a phenomenon in which people seem to gather together out of nowhere to create an instant event -- and then melt back into the crowd when it's over.
This "flash mob" was the result of days of organization via e-mails, text messages and the social-network Web sites Facebook and Twitter.
"Flash mobs" are "very surprising," said Jessi Carrier, 23, one of the main organizers of Thursday's protest. "People enjoy being a part of them. They kind of transform the space where they take place."
Most of the "flash mob" gathered around the giant rock of Kazuo Matsubayashi's sculpture "Asteroid Landed Softly," waiting for the pre-arranged signal to fall down.
That signal was supposed to go off at 8 p.m. sharp. It was delayed because Carrier and her cohorts, trying to unfurl their banner, were dodging the garage's security guards. Carrier said they also didn't want to compete with the show's opening act, N.A.S.A.'s Intergalactic Circus.
The protesters stayed on the ground for five minutes as others in the crowd snapped cellphone pictures or tried to walk past. At 8:22, the whistles sounded again, everyone got up -- and many of them disappeared smiling into the concert audience.
"I don't think there was anybody who didn't notice," said Flora Bernard, one of the "flash mob" organizers. "As long as they're paying attention, that's enough."
The protest was organized by Peaceful Uprising, which aims to help "those who engage in nonviolent direct action" against climate change, according to its Web site.
One of Peaceful Uprising's founders is Tim DeChristopher, the University of Utah student still awaiting his court date on federal charges of disrupting a Bureau of Land Management auction of oil and gas leases last December. DeChristopher attended the protest, but stressed he was not one of its organizers.