An action-packed week on Wall Street ends with a bang as index-tracking funds are set to reshuffle $250 billion of shares, just as a “triple witching” trading event hits.

European markets traded lower on Friday after Asian stocks surged, as a rally driven by the Federal Reserve’s big cut to interest rates faded. Germany’s DAX lost 1.0% to 18,813.20 and the CAC 40 in Paris slipped 1.

For all the nail-biting about the economy over the past year, investors had it easy: a 5% yield on short-term U.S. debt, one of the safest investments in the world. Now, the times they are a-changin’—again.