Why does the sniper decide to risk taking a look at the corpse of the enemy sniper?
The Republican sniper may have had an idea that the Free State sniper would be someone he recognized. Many of the men who fought in the Irish Civil War had served together in the Irish Republican Army which had waged war against the British, gaining independence in 1921. A dispute arose between factions of the IRA and in 1922, they split. The protagonist sniper in Liam O'Flaherty's short story remained loyal to the Republican army and believed that Ireland should have full autonomy, while the Free State soldiers, including the antagonist sniper, were in agreement with the Anglo-Irish Treaty which made Ireland part of the British Commonwealth. O'Flaherty suggests that the two snipers may have served together and the Republican sniper is curious because his enemy had been a good shot:
He decided he was a good shot, whoever he was. He wondered did he know him. Perhaps he had been in his own company before the split in the army. He decided to risk going over to have a look at him.
Of course, he did know the enemy, who turned out to be his brother. Apparently, as in any family, the politics of the two brothers turned out to be quite different. The fact that it was his brother may not have been that surprising to the Republican sniper as he was probably well aware of his own brother's marksmanship.