Ulam tells some funny stories, many of them involving his friends Johnny von Neumann and Enrico Fermi. Here is a taste of Fermi's wit (p.164):
Once Segrè, who was very fond of fishing on weekends in the streams of the Los Alamos mountains, was expounding on the subtleties of the art, saying that it was not easy to catch trout. Enrico, who was not a fisherman, said with a smile, "Oh, I see Emilio, it is a battle of wits."
There is a wonderful picture of Ulam on the web (here).