The Mussa puzzle refers to the existence of a large and sudden jump in the volatility of the real exchange rate after the adoption of a floating exchange rate regime in 1973. It is a central piece of evidence in favour of monetary non-neutrality. In contrast to conventional wisdom, this column argues that the puzzle cannot be explained with sticky prices, and instead provides strong evidence in favour of monetary transmission via the financial market. This has important consequences for the design of optimal monetary and exchange rate policy.