In 10 bone-shaking minutes on Thursday the Dow Jones Industrial Average - representing the 30 most venerable US firms - briefly lost almost a tenth of its value.
Open-jawed investors blanched as the pensions and savings of millions of Americans were decimated, along with the livelihoods of countless more.
Days and a partial recovery later, the most fundamental question has still not been answered: What happened?
Concerns about Europe's debt crisis no doubt contributed, but few analysts believed worries about Greece's fiscal malfeasance - as serious as it may be - would cause US equities markets to go through a near-death experience.
