As fears of an American recession spread, stockmarkets around the world have been jittery. The moves have been the wildest of all in Japan. On August 5th the Topix plunged by 12% in its worst performance since 1987; the yen had climbed from its weakest point in 37 years. The next day, stocks swung back, rising by 9%, as investors snapped up stocks that had plunged in value. The sharp moves carry implications not just for Japanese investors and firms. The country’s financial heft means that they could become a source of further volatility in nervous global markets.