In June 2003, more than 130 people gathered around one expensive rug on the ninth floor of Macy’s in Manhattan. Each told the confused salesperson the same story: they lived together in a warehouse on the outskirts of New York and were shopping for a love rug. Then they left. It was the first successful flash mob, and its architect was Bill Wasik, a senior editor at Harper’s Magazine who wanted to see whether downtown trend chasers would show up for something meaningless if it felt exclusive.

This episode follows the idea from that cynical experiment to its darker afterlife. Wasik’s first attempt failed when the target store was tipped off, so he staged participants in four Manhattan bars and handed out the real location on slips of paper. The craze spread worldwide, drew pushback from police and city officials, and by around 2011 had mutated into flash robs, with groups of teenagers overwhelming stores. A 1973 Larry Niven story had predicted nearly all of it.

• Sociologists separate a flash mob, which is deliberately pointless, from a smart mob, a term Howard Rheingold coined in 2002 for gatherings with a political or practical goal.
• Other early Wasik events included 200 people applauding for exactly 15 seconds in a Hyatt Hotel lobby and a crowd posing as lost bus tourists in a SoHo shoe boutique.
• Larry Niven’s story Flash Crowd imagined cheap teleportation letting thousands of people appear at a minor incident and turn it into a riot.
• The phrase flash mob was also used in 19th century Tasmania for a subculture of female prisoners, a coincidence with no link to Wasik.
• Duke psychologist Mark Leary ties flash robs to deindividuation, the anonymity of a crowd that lets people do what they would never do alone.