Whenever a new outbreak of avian flu is reported people eat less chicken, not just from the infected farm, but from anywhere. They clearly feel they have learned something new and nasty about chicken, and that it has become riskier, even if the chickens themselves are the same, somewhat confused-looking birds that they were before. This week something similar happened in the world’s investment markets.

The price of almost every risky asset fell, almost everywhere in the world, with most big stock markets down by 4-6 per cent. Yields on government bonds went down, yields on corporate and high-yield bonds, which carry greater credit risk, went up. Currencies with low interest rates, such as the Swiss franc and Japanese yen, rose and volatility increased all round.