Liam O'Flaherty presents the protagonist of his short story, "The Sniper," as a fanatic:
...his eyes had the cold gleam of a fanatic.
The sniper's behavior, so driven and blinded to the value of human life, shows him to be little more than a killing machine. He is like a war-ravaged soldier who has seen a great deal of death but knows how to survive. He is very good at what he does, as seen when he kills the man in the tank and the woman who tries to identify his whereabouts on the roof.
The sniper is not invincible: another excellent sniper shoots him in the arm, and the reader might believe he is incapacitated. Nothing is farther from the truth: what he lacks now in physical capability he makes up for in sheer determination.
His reaction to killing the tank driver and the informer, and what he experiences when he takes out the sniper, are very different. (We might even see this as foreshadowing.) Where the earlier deaths were handled in a business-like fashion, with this death, the sniper first emits a cry of joy over his success, but then it's as if he becomes sick. Perhaps he feels the regret a hunter feels when killing a beautiful, but dangerous animal.
First the sniper begins to shake, and his desire to hunt flows out of him: he experiences sadness, "remorse," for what he had done. He begins to sweat, and the sight of the dead man on the ground below makes him sick. He seems to be in shock as he starts to shiver and talk to himself, hating the war and all that comes with it.
The sniper looked at his enemy falling and he shuddered. The lust of battle died in him. He became bitten by remorse. The sweat stood out in beads on his forehead. Weakened by his wound and the long summer day of fasting and watching on the roof, he revolted from the sight of the shattered mass of his dead enemy. His teeth chattered, he began to gibber to himself, cursing the war, cursing himself, cursing everybody.
The sniper takes the gun in his hand and throws it away from him, sickened by what he has done.
He looked at the smoking revolver in his hand, and with an oath he hurled it to the roof at his feet.
The gun goes off and nearly hits the sniper in the head, and this near-death experience shakes him out of his feelings of shock. His laugh is probably the nervous kind that comes from a scrape with death. His initial reaction seems to subside, but foreshadows the story's end. O'Flaherty's sudden ending does not allow for the responses listed above, but as readers we can imagine that he feels these things all over again when he discovers that he has killed his brother. A deeper reality of the horror of war would wash over the sniper and one would imagine the fanatic gone, and the mere shell of a man in his place, trying to comprehend the enormity of his actions: reactions not of a fanatic, but of a caring man who has lost his brother to war: in a most painful way.
With his enemy dead, the sniper feels regret at what he has done.