The numbers flashing on trading screens on Aug 5 were shocking even to market veterans. In Tokyo, the Nikkei 225 was down 12 per cent. In Seoul, the Kospi index sank 9pc. When the opening bell rang in New York, the Nasdaq plunged 6pc in seconds. Cryptocurrencies sank; the VIX, a gauge of stock market volatility, skyrocketed; and investors piled into Treasury bonds, the safest asset of them a