Radio comedian Don McNeill staged experiments in the lobby of Chicago's Merchandise Mart to test whether people would still fall for some of the oldest April fool gags. He discovered that 20 of the first 25 people who saw a bill fold lying on the floor stooped to pick it up, only to have it yanked away. In addition, McNeill set up an aquarium with a sign "Invisible Peruvian fish." He asked spectators to estimate the length of the fish. Fifty-six of the spectators turned in written estimates. (For more about the "invisible fish" prank, see Brazilian Invisible Fish.) [The Galveston Daily News, Apr 2, 1940.]