Question about Edward Thomas's "The New Year"?

I'm annotating the poem and trying ti figure out why the poet constantly refers to the old man as animals? All I can get is that it dehumanizes the man, but if this is the speaker's goal, then what has he achieved by doing this? The speaker does not seem to dislike the man, and the encounter they have is quite friendly, so this makes me wonder; why compare the old man to a "tripod", "less like a man than his wheel-barrow in profile was like a pig" and "like a tortoise"?