Alliteration fills the poem with rough, rugged music befitting its main character: the wild boar. This alliteration often uses plosive sounds like /b/, /p/, and /t/. Such consonants require the mouth to block and then expel air, and here they make the poem's language more forceful and emphatic.
For example, listen to some of the phrases the speaker uses to describe the boar and his mountain home:
black-maned wild boar
Plowing with his snout on Mal Paso Mountain.
The old black-bristled boar,
Said the old father of wild pigs,
Plowing the fallow on Mal Paso Mountain.
All those /b/ and /p/ sounds evoke the boar's huffing, grunting effort as he snuffs out food. Towards the poem's end, the spiky /t/ sound in "Tusking the turf" also conveys the sharpness of the boar's tusks.
The boar's actual speech is full of plosive sounds too, making him sound passionate and strong-willed:
"The world's in a bad way, my man,
And bound to be worse before it mends;
Better lie up [...]
"Keep clear of the dupes that talk democracy
And the dogs that talk revolution,
Drunk with talk [...]
The heaving /b/ and /d/ sounds and the sharp /t/ sounds convey the boar's frustration and disappointment with the state of the world. Note, too, how alliteration links "dupes" with "democracy"—that is, people who have been deceived with the ideology that deceives them.
There's some sibilant alliteration in the poem as well. Listen to lines 8-9:
The old monster snuffled, "Here are sweet roots,
Fat grubs, slick beetles and sprouted acorns.
These sounds evoke the very "snuffling" described, making the poem's imagery more striking for readers.