The noun “cud” is the partially digested food regurgitated by cows for further chewing and digesting. Owen applies the word to give the image of blood that “come[s] gargling from the froth-corrupted lungs” an even more jarring impact.
"the white eyes writhing..."See in text(Text of the Poem)
The verb “to writhe” means to twist or contort one’s body, usually from pain or discomfort. However, Owen uses the word to describe the dying soldier’s eyes, as opposed to his entire body. As a result, the vivid visual imagery carries an even greater emotional impact.
The noun “ecstasy” commonly refers to intense happiness, joy, or passion. However, Owen’s use of the word subverts the common meaning to represent the overwhelming, frantic efforts of the soldiers to shield themselves from a chemical attack.
In this context, the adjective “lame” refers to a condition or an injury that reduces a person’s ability to walk. Owen portrays the soldiers as being so exhausted and beaten down from constant violence that they struggle to walk.
The adjective “knock-kneed” refers to a condition in which a person’s legs curve inward at the knees, causing his or her feet and ankles to remain apart even with knees touching. Here, this word choice emphasizes the image that the simile of the soldiers walking “like old beggars” conveys—that they are weighed down by their sacks and their conditions.
