And the cry of hounds came tumbling invisibly with their echoes down through the draggle of trees,
Swinging across the wall of dark woodland,
The stag dropped in to strange country.
And turned at the river
Hearing the hound-pack smash the undergrowth, hearing the bell-note
Of the voice carried all others,
Then while the limbs all cried different directions to his lungs, which only wanted to rest,
The blue horsemen on the bank opposite
Pulled aside the camouflage of their terrible planet.
And the stag doubled back weeping and looking for home up a valley and down a valley
While the strange trees struck him and the brambles lashed him,
And the strange earth came galloping after him carrying the loll-tongued hounds to fling all over him
And his heart became just a club beating his ribs and his own hooves shouted with hounds' voices,
And the crowd on the road got back into their cars
Wet-through and disappeared.
The stag, in Hughes' imagination, loses its sense of self, and seems to have absorbed the violence, with the heart a club assaulting its ribs, and the hooves ‘shouting’ like the dogs.  Its own body is now merged with the hunt and the killing. The reader understands that this is a metaphor for the killing of the prey.
The Stag