Seamus Heaney comes from a long tradition of Irish poets rooted in the music of both English and Gaelic languages. As we see in this poem, it's tough to escape your roots! Though Heaney breaks the mold a little bit in this poem by chucking any sense of a rhyme scheme out the window, rhyme is still abundant throughout the poem, as well as other sound effects. Let's check it out, shall we?
Probably our first encounter with rhyme was nursery rhymes, where the words mirrored each other perfectly for the familiar, hard rhyming sound of cat and hat, dog and hog, pig and wig, book and hook, etc. These rhymes are loud and proud; you can hear them a mile away.
Sometimes though, poets want to be a little softer with their rhyming, so you're not distracted by the rhyme while you're reading the rest of the poem. It's kind of like how you might not want to wear a leopard print jacket if you want people to pay attention to your black pants. Half rhyme offers just the solution. The words sound very similar to one another, but don't rhyme perfectly. Here are a few from "Digging" (they're easiest to identify when read aloud, so all together now):
thumb/gun; ground/down; flowerbeds/bends; bog/sods; edge/head.
Hear how similar the words are? Matching vowel sounds with similar consonant endings, but there's always something a little askew. At first, you might miss the slant rhymes, but eventually your ear will recognize that there's something familiar going on.
So what's the point of all that slant rhyming? Why not just have it rhyme outright? For one thing, it keeps awesome readers like us from getting distracted by all the noise. And for another, it creates a subtle rhythm in the poem, kind of how, say, digging, is kind of rhythmic, but not perfectly so. It's a lovely, if not always noticeable, effect.
Heaney uses full rhyme (the rhyme we're accustomed to, where both words rhyme perfectly) sparingly throughout the poem, and often sets them far apart from one another so they don't echo too loudly. Here are two examples:
These rhymes totally slow us down. It's like a bell tolling slowly at the end of each line. We're forced to pay attention, and revisit the line before, when the rhyme first started.
Internal rhyme just means that both words in the rhyme don't come at the end of the lines. So while one of the words might be the last in the line, the other is somewhere in the middle of the same line, or a different line within the stanza. They can be full rhymes or slant/half rhymes. These are best identified by example, so let's dig some up:
snug/gun; knee/firmly; men/them
In a way, these have a similar effect as slant rhymes in general, because they create a not-too-obvious repetition of sound. They don't beat us over the head with it, but they're there to remind us that there's music underneath all these words.
Alliteration refers to the use of words near each other that all begin with the same letter or sound. Like this: big, bad, banana, or pork with pickled pimentos. When the alliterative words begin with "s," they're also called sibilant. Sibilant words sound like a snake hissing: "Sally sells sea shells down by the sea shore." Those are exaggerated examples, and in "Digging," Heaney is much more careful with his alliteration so his poem in no way resembles "Peter Piper picked a peck..." Thank goodness for that! Here are Heaney's examples:
spade sinks; gravelly ground; tall tops; buried the bright; squelch and slap of soggy; curt cuts
Notice how the repeated sounds in this case make you read a bit faster. They're almost sing-songy.
Consonance is the repetition of hard, consonant (opposite of vowel) sounds in a close area (within the same line or stanza). In this poem, sometimes consonance works together with alliteration to make a big, firecracker of a sound.
Assonance is like consonance, but repeats vowel sounds instead of consonant sounds. Because Heaney is so crafty, sometimes the two work together to pack a double whammy of sound play.
The repetition of all those vowels reminds us of long notes in a song. They cause us to linger as readers, to sink in and revel in the music.
We'll end on that note, but if you continued to hunt, we're sure you'd find more. There are so many small reverberations of sound in this poem: it's like standing in the forest on a summer night listening to all the different tree toads, bullfrogs, crickets, and cicadas chirp out their own symphony, with Heaney as the composer and conductor all rolled into one.