This is certainly a tremendous poem which owes its crackling energy in part to the way in which Plath combines a number of different techniques to make it appeal to our hearing. Consider the way in which Plath utilises a bewilidering array of end and internal rhymes, which are both exact and slant, combined with alliteration, repetition, consonance and assonance. Look at the following example:
Soon, soon, the flesh
The grave cave ate will be
At home on me
Note the internal rhyme in "grave cave" and the repetition of the vowel sound of "a" in the middle line and also the end rhyme of "be" and "me." It is the use of so many techniques combined with the gripping narrative that emerges in this poem that imbues it with such energy that drives us forward to the ending.