In the "Form and Meter" portion we talked a bit about how the rhythm of the poem is established by even iambic pentameter, and how the consistent rhyme scheme expertly tied everything together. But, this is Heaney we're talking about here, so every element of sound matters in his poetry.
Consonance: consonant sounds close together in line make for a real earful. Check out line 9, "Sent us out with milkcans, peatins, jam-pots." All those italicized letters make for really rich sounds in the mouth.
Similarly, Heaney likes to use alliteration, which is the close repetition of the same letter at the beginning of a word. Line 10 has three b words. In fact b sounds pop up a lot all throughout this poem. He's also really fond of ck sounds. Count how many you can find. We count 24! So instead of airy, light language, Heaney prefers the physicality of harder, harsher sounds, perhaps to reflect the physicality in the poem itself.