We go back in time. It's 1943, before Yossarian is stationed at Pianosa. He is in basic training at Lowery Field in Colorado. He calls in sick to avoid P.E. class claiming a liver condition. Some things never change.
The officers see through this ruse and want to tell him to get lost but can't because of regulations.
They hospitalize him for ten days. Afterwards, he seems to be healthy again and they tell him to leave.
Yossarian is saved in the nick of time by a fellow patient who suddenly shouts, "I see everything twice."
There is panic. The doctors can't figure out what's wrong with him and so they quarantine everyone for another fourteen days.
Yossarian spends Thanksgiving in the hospital; it is the most rational Thanksgiving he has ever had. He vows to spend his next Thanksgiving in a hospital, too.
He does not. He spends his next Thanksgiving with Lieutenant Scheisskopf's wife in a hotel room.
They have an argument about God.
Even though Mrs. Scheisskopf doesn't believe in God, she is appalled by Yossarian's pessimistic depiction of Him as "a country bumpkin" who is completely incompetent. She breaks down crying.
Yossarian considers it the most illogical Thanksgiving he has ever spent.
Then he goes back in his mind to the previous Thanksgiving and we hear a different story – now Yossarian is the one who shouted, "I see everything twice."
Then he plays with the incompetent doctors.
They inform him that the family of a soldier who just died has come to see him. Yossarian agrees to masquerade as the dying soldier for the benefit of the family – a father, mother, and brother.
When they visit him, they don't recognize that he is not their son and the visit becomes surprisingly emotional, leaving Yossarian in tears.