I saw a line of people with umbrellas at the top of the steps leading from the Dom cathedral to the station, standing quietly, looking down an oddly empty square. Then I noticed occasional bursts of laughter. People were waiting for unwitting pedestrians to step into the huge but hard-to-see puddle that had formed after a day of rain. This waiting and laughing went on for at least an hour and a half, and was still going even when I left after dark. No one who was laughed at seemed to mind.