Repetitions of sounds are among a group of stylistic devices called “figures of speech” that are characteristic of the heightened diction of poetry. Repetition of consonants is called consonance and repetition of vowels is called assonance. Repetition of sounds at the beginning of words is “alliteration” and repetition of final syllables at the ends of poetic lines is rhyme.
In A Display of Mackerel,” these devices are used is several places, e.g. alliteration in “barred with black bands” and again in “soapbubble sphere,/ think sun on gasoline./ Splendor, and splendor…”
These devices are used for two reasons. One is aesthetic. The other is to suggest that words with similar sonic characteristics stand in a close relationship to one another within the structure of the poetic meaning.