you keep telling these war stories you must have killed someone
of course not
time for your shift
Tim O' Brian describe to his daughter that hes never killed anyone secretly hoping she asks again at a more mature age so that he could share.  
...
In this scene The author goes in dept and describes how him and the guards took shift to sleep through the night.
that was a good kill besides he would have died anyway 
He also describe how the man that emerged from the fog on his shift was a tall and good looking young man with an ammo belt and a gun with the muzzle to the ground. 
yeah like imagine what he would've done to us 
Without conscious thinking in ablink of an eye he throws the grenade at the soldier.
Time O' Brian starts to feel the weight and growing uncomfortable feeling is his stomach as he reflects on what just happened.
After he returns to base his comrades try to justify and reconcile on him on how what he did was a good thing but he couldn't get over the guilt and his mind was still racing.