Central bankers are always vigilant. That is their job. But if they forget to remind everyone that they are still on their vigil, markets can take it as an excuse to make some trades.

Thursday’s rise in the European Central Bank’s refinancing rate was universally expected and, consequently, had almost no discernible effect on foreign exchange markets. But when Jean-Claude Trichet, ECB chairman, gave his press conference after the rate decision, everyone wanted to know if he would describe himself as “vigilant”. He did not. He also removed a reference to the need in future for “progressive” withdrawal of monetary accommodation.