Lee Strunk and Dave Jensen get in a fight over a missing jackknife. Dave Jensen breaks Strunk's nose so hard that Strunk has to be flown back to the rear.
When Strunk returns two days later, Dave Jensen gets nervous. Paranoid. He keeps away from Strunk and feels like he's always under attack.
One afternoon, he starts shooting his gun in the air, yelling Strunk's name. All the other soldiers hit the ground (of course).
When he runs out of ammo, Jensen puts his head in his arms and refuses to move for two or three hours.
That night, he breaks his own nose with a pistol.
Then he goes up to Strunk and asks if they're even. Strunk says they are.
Later, though, Strunk is still laughing, saying that Jensen is crazy, and that he'd actually stolen Jensen's jackknife.
It's kind of unclear whether Strunk means that Jensen is crazy to forgive Strunk for stealing his jackknife and that he didn't need to break his own nose to be even, or that Jensen is just crazy in general. Knowing this book, it's probably both.