Seamus Heaney’s poem titled “Bog Oak” employs a number of poetic techniques and devices in support of its themes and meanings. Among those techniques are the following:
Lines 1-28: the poem is unusually narrow. Many lines have only four syllables, so that the poem almost resembles, physically, the rafter it describes.
Line 2 begins with the very heavily accented verb “split,” which is further emphasized because of the use of enjambment in line 1.
Lines 3-4 use a catalogue, or series, of adjectives, so that each adjective is strongly emphasized, especially the third and final one, which is also the longest of the three in the number of syllables it contains. The noun that follows this series of adjectives receives strong emphasis precisely because it is so long delayed, and the emphasis seems all the more forceful when it does come since the noun is monosyllabic.
Line 8 uses alliteration to call special attention to the unusual term “creel fillers,” a term whose precise meaning is unclear, although obviously it implies certain kinds of laborers. (The term was associated with child labor in cloth factories in the nineteenth century.)
Line 10 uses a kind of paradox when it refers to “hopeless wisdom,” since we normally think of wisdom as providing hope.
Lines 13-18 use various kinds of repetition to enhance the sonic appeal of the poem, such as the echo of sounds in “far” and “cart,” the internal rhyme of “track” and “back,” and the actual rhyme of “no,” “no,” and “mistletoe.”
Line 18 uses especially strong assonance in the repeated long “o” sounds of “‘oak groves,’ no.”
Line 22 uses an historical allusion in the reference to sixteenth-century English poet Edmund Spenser, a resident of Ireland.
Lines 26-27 use textual allusion by apparently echoing the words of Spenser, which indeed turn out to be particularly gruesome words from his prose dialogue A View of the Present State of Ireland. In this text, one English colonist proposes that the Irish should be suppressed by being starved. He claims to have witnessed the success of such a policy already in Ireland, saying of the desperately famished Irish,
Out of every corner of the woods and glens they came creeping forth upon their hands, for their legs could not bear them. They looked like anatomies of death; they spake like ghosts crying out of their graves; they did eat the dead carrions, happy where they could find them; yea, and one another soon after, insomuch as the very carcasses they spared not to scrape out of their graves.
In other words, not only did the hopeless Irish eat the rotting flesh of animals, but eventually they even ate one another and also even ate corpses retrieved from graves.
What does this horribly gruesome allusion have to do with the larger themes and meanings of the poem? Presumably it is there to caution us not to romanticize Ireland’s past. Irish bogs can yield up fine timbers that can be used in building thatch-roofed barns or cottages, but the Irish past can also yield up truly disgusting remnants as well. The piece of oak on which the poem focuses during its first half was taken out of a bog and prized, but the poem ends with the sickening image of corpses being dug out of their graves to be eaten. To say that the ending of the poem is ironic is a highly radical understatement.