We find out it is Yossarian's fault that Major ------- de Coverley is missing and cannot save him (because Yossarian moved the bomb line over Bologna and the Major went there, thinking it was safe).
It is also his fault that Nately fell desperately and futilely in love with his prostitute. Yossarian set up the blackjack game at the enlisted men's apartment where the two met.
So basically, everything is Yossarian's fault.
Nately has sex with the indifferent prostitute for the first time there. When she leaves, Nately despairs.
When his friends advise him on how to get her back, Nately responds by asking them not to call her a whore.
Aarfy makes fun of Nately relentlessly.
Aarfy's fearlessness in the middle of flak fire amazes Yossarian.
Aarfy is with Yossarian when Yossarian injures his leg at Leghorn. Yossarian shouts at Aarfy that he has lost his balls, but Aarfy pretends to be deaf. Yossarian passes out. When he regains consciousness, McWatt is taking care of him.
In the hospital, Dunbar has changed his name to A. Fortiori. (This is a satire of the Latin a fortiori meaning "for an even stronger reason" or "even more so.")
Dunbar leads Yossarian away from the doctors and reveals that he has been "pulling rank," which in this particular Catch-22 case means changing his name and rank to see Yossarian. He advises Yossarian to try it.
Yossarian does and becomes Warrant Officer Homer Lumley.
Nurse Cramer yells at Yossarian to get back to bed. She tells him that his injured leg is the property of the U.S. government and that he should obey the doctor's orders.
Yossarian tells her to "screw!" meaning "go away." She hits him in the face and then goes running to Nurse Duckett, crying.
Nurse Duckett is not amused. She takes Yossarian by the ear and puts him back to bed.