For a good few hours on April 9th, disaster beckoned. Share prices had been falling for weeks. Then the market for American Treasury bonds—normally among the safest assets available—started convulsing, too. The yield on ten-year Treasuries leapt to 4.5% (see chart 1), up from 3.9% days earlier. That meant bond prices, which move inversely to yields, had cratered. The failure of both risky and supposedly safe assets at once threatened to destabilise the financial system itself.