Always they must see these things and hear them, Batter of guns and shatter of flying muscles, Carnage incomparable and human squander Rucked too thick for these men's extrication.
Therefore still their eyeballs shrink tormented Back into their brains, because on their sense Sunlight seems a bloodsmear; night comes blood-black; Dawn breaks open like a wound that bleeds afresh —Thus their heads wear this hilarious, hideous, Awful falseness of set-smiling corpses.
Owen's chilling contrast between "Treading blood" and "lungs that had loved laughter" echoes a regular theme in his works, that the men who gave themselves for the war had once been amiable and friendly people before the dead "ravished" their minds.
The third stanza describes how those who survived the war live now with shell shock, in that scenes from the battlefield insert themselves into everyday life; sunlight is a "blood-smear" on a window, then night falls "blood-black" - they cannot escape the sight of blood.
The macabre tone of the poem is added to by the image of hallucinations of "set-smiling corpses", describing the "hilarious, hideous" faces of the patients as they remember.