In Chapter 9, what does the second C.I.D. man almost tell all the men on the base and how is it ironic?

A C.I.D. man passes by, and although Yossarian reassures Milo that the officer is only looking for “Washington Irving.” Milo says that it is a trick to make him confess about his black market operations. Yossarian infuriatingly declares that he will not fly the 55 missions and will go see Major Major. Milo replies that doing so is futile, so Yossarian says he will return to the hospital. Milo then asks Yossarian to give him one package of pitted dates; in return, he gives Yossarian a quarter of McWatt’s yellow bedsheet.