Rhetorical devices are used by authors to have an emotional effect on the reader.  Some of those devices in this story are imagery, the use of sound, and the surprise ending (irony).  

There is so much imagery and sound in this story that draw the reader into it.  The reader is completely immersed in this story in part due to its wonderful detail and use of sound.  For example, the author uses real places in the story and describes them in much detail.  He also describes the sounds of the bullets whizzing by, the lighting of the cigarettes he smokes, the pain he feels when he is shot.  eNotes states that:

Throughout Dublin, the machine guns and rifles “broke the silence of the night, spasmodically, like dogs barking on lone farms.” When the sniper gets shot and drops his rifle with a clatter, he “thought the noise would wake the dead."

 The details in this story and the use of the sound makes the setting much more realistic and feasible.  The readers feels as if he/she is on the rooftop with the sniper observing what he/she is.

The surprise ending is emotional and heart-wrenching.  The other sniper that he has killed is his own brother.  The reader is not expecting this ending at all, so the complete shock of the other sniper being his brother is simply mind-boggling.