A day for pranks, practical jokes, and sincere efforts to make fools of the gullible, April Fools Day is an international celebration of silliness. The origins of the holiday have been disputed, but the most coherent explanation relates to the change from the Julian to the Gregorian calendar. Yet even this explanation is easier to take if the person describing it wears a floppy multicolored hat with numerous jangly bells attached to the ends.