This is what editor Anthony Thwaite has to say about it:
When Ted Hughes was an undergraduate at Cambridge in the early 1950s, he switched from English to Archaeology and Anthropology; and though I feel Hughes’s anthropological interests were probably stronger than his archaeological ones, there seems to be a strong flavour of what one could call linguistic archaeology in his poem Thistles. Remember that Hughes came from a partly Viking enclave of Yorkshire. (p46)
by Ted Hughes
Against the rubber tongues of cows and the hoeing hands of men
Thistles spike the summer air
And crackle open under a blue-black pressure.
Every one a revengeful burst
Of resurrection, a grasped fistful
Of splintered weapons and Icelandic frost thrust up
From the underground stain of a decayed Viking.
They are like pale hair and the gutturals of dialects.
Every one manages a plume of blood.
Then they grow grey like men.
Mown down, it is a feud. Their sons appear
Stiff with weapons, fighting back over the same ground.