The so-called flash crash of May 6 saw the Dow Jones Industrial Average fall almost 600 points in five minutes. It recovered just as quickly. The official investigation into the crash has not blamed the expected culprits, high-frequency traders, but an old fashioned programmed trade. However, James Mackintosh, investment editor, suggests another old villain, sentiment, played its part: without the jitters in the market there may not have been such a fall.