what happen to ishmael during his first experience with killing?

From the text:

The corporal gave the signal with a pistol shot and I grabbed the man’s head and slit his throat in one fluid motion. His Adam’s apple made way for the sharp knife, and I turned the bayonet on its zigzag edge as I brought it out. His eyes rolled up and they looked me straight in the eye before they suddenly stopped in a frightful glance, as if caught by surprise. The prisoner leaned his weight on me as he gave out his last breath. I dropped him on the ground and wiped my bayonet on him.