1)In the second stanza, most of the soldiers succeed in putting on their clumsy gas masks. Someone, however, is still crying out for help, unable to move quickly and easily enough to put on his mask, as if he's stuck in fire or lime.
2) Through the misty green panes of the gas mask, the poet saw his friend who looked as if he were drowning in the deadly gas. [The greenish color of the panes in the eyepieces of the gas mask made everything seem green. I always imagine this as if he were about 20' under the ocean's surface where everything looks greenish.]
3) The memory of his dying friend returns in his dreams, and he cannot stop them. The poet cannot help seeing his friend, lunging at him as he asks for help and then is dying.
4) His friend moves towards him, like a guttering candle which is about to go out, choking and drowning.
In the third stanza, the poet wonders if the readers can imagine walking behind a wagon into which their dying friends had been thrown once they couldn't walk.
5) He wonders if readers can see his friend's face, with its skin starting to fall off, and his white eyes writhing.
6) He then wonders if readers can hear the gargling sound as his friend tries to breathe through all the blood in his lungs.
7) “Obscene as cancer, bitter as the cud of vile, incurable sores of innocent tongues” (<~~All those descriptions are there to emphasize how repulsive and awful the effects of gas and bombs are. I don't know that they should be rephrased. You might just refer to the obscenities of the results of war.)
If the reader could experience the horror of the war, he wouldn't tell his children the old lie that it is sweet and fitting to die for one's country.
**Have you ever seen "The Last Judgement" on the end wall in the Sistine Chapel?
Michaelangelo is said to have painted his own face into this; see the image that looks like someone's skin has been peeled off? This is what Owen is trying to describe here: that one of the effects of this gas was that his friend's face looked as if it had been peeled off him. It's absolutely dreadful.