Because of his many different engagements, von Neumann had to be especially concerned with secrecy, but he took this with good humor. As he was traveling a lot, he was accompanied by two “gorillas.” He met with Stanislaw Ulam on the Chicago railway station and recruited him for the work at Los Alamos. However, von Neumann could not reveal the exact nature of work, nor the location. He could only tell Ulam that it was in the southwest. Ulam told him: “I know you can’t tell me, but you say you are going southwest in order that I should think that you are going northeast. But I know you are going southwest, so why do you lie?”

István Hargittai, The Martians of Science: Five Physicists Who Changed the Twentieth Century, Oxford, 2006, p. 123