Rumors spread panic for a reason

Rumors of stabbings in Guangzhou, Guangdong province, led to panic among residents last week, a day after a knife fight between food vendors in Changsha, Hunan province, left six people dead. On March 14, hours after the Changsha violence, dozens of shoppers at a busy mall in Chengdu fled in panic because of rumors that some people had gone on a stabbing spree. Seemingly, people were on the edge after the knife attack at Kunming, Yunnan province, in which 29 people were killed and 140 injured two weeks ago.

A good example of how we can be fooled into collective delusion by rumors is the case of the Seattle "windshield-pitting epidemic". In 1954, car owners north of Seattle, Washington state, began to notice pits on their windshields, leading them to believe that a common causative agent was at work. Residents and the press began to attribute the pitting to everything from sand flea eggs to nuclear bomb testing. Police initially believed they were the handiwork of vandals using BB guns. But since the phenomenon was observed even in nearby towns and eventually metropolitan Seattle, more and more reports were phoned in and newspapers began to feature the story.

Several theories for the widespread damage were postulated, including the fact that a new Navy radio transmitter was producing waves that caused the windshields to shake. The speculations included cosmic rays, a shift in the earth's magnetic field and supernatural gremlins. But after Sergeant Max Allison of the Seattle police crime laboratory said the pitting reports consisted of "5 percent hooliganism, and 95 percent public hysteria", the phenomenon suddenly stopped.