A Q & A with Author Charles Duhigg What sparked your interest in habits? I first became interested in the science of habits eight years ago, as a newspaper reporter in Baghdad, when I heard about an army major conducting an experiment in a small town named Kufa. The major had analyzed videotapes of riots and had found that violence was often preceded by a crowd of Iraqis gathering in a plaza and, over the course of hours, growing in size. Food vendors would show up, as well as spectators. Then, someone would throw a rock or a bottle. When the major met with Kufa's mayor, he made an odd request: Could they keep food vendors out of the plazas? Sure, the mayor said. A few weeks later, a small crowd gathered near the Great Mosque of Kufa. It grew in size. Some people started chanting angry slogans. At dusk, the crowd started getting restless and hungry. People looked for the kebab sellers normally filling the plaza, but there were none to be found. The spectators left. The chanters became dispirited. By 8 p.m., everyone was gone. I asked the major how he had figured out that removing food vendors would change peoples' behavior. The U.S. military, he told me, is one o