After fleeing battle and witnessing his friend Jim’s death, Henry finally returns to his regiment sporting a head wound he sustained in an altercation with a fellow Union army soldier. Because Henry doesn’t want his comrades to realize that he fled or find out about the humiliating circumstances of his wound, he pretends that he was hit by a Confederate bullet. The response of the regiment’s corporal, who treats the wound, is an example of dramatic irony. Looking at Henry’s head, he says,
Yeh’ve been grazed by a ball. It’s raised a queer lump jest as if some feller had lammed yeh on th’ head with a club.
The corporal isn’t at all suspicious of Henry, and makes this remark offhandedly. But by remarking that it looks like someone “lammed”—in other words, hit—Henry with a club, he’s describing exactly what happened, since the Union soldier hit Henry with his rifle. This moment constitutes dramatic irony because it capitalizes on the difference between the corporal’s understanding of the situation and the knowledge about what really happened that Henry and the reader possess.
In the midst of a largely grim novel, this moment of irony provides some much-needed comic relief: everyone in the regiment pretends to be an expert on war, but no one really knows how to distinguish between courage and cowardice. Also, the care with which the corporal attends Henry functions as a rebuke of Henry’s comparatively ungracious attitude. Until now, he’s been more focused on comparing himself to his fellow soldiers than worrying about their safety, and he’ll only learn to truly prioritize his comrades at the end of the novel.