The poem uses repetition to create rhythm and musicality while mirroring the way stories get passed down from one generation to the next.
Lines 1-2, for example, use a combination of anaphora, epistrophe, and more general parallelism:
Aunt Sue has a head full of stories.
Aunt Sue has a whole heart full of stories.
The repetition underscores who is telling these stories (Aunt Sue) and how many of them there are (she's "full" of them). Because these lines are almost identical, the repetition also highlights the few words that don't repeat: "head" and "whole heart." The shift from "head" to "heart" suggests these stories aren't just something Aunt Sue thought up for entertainment; they're memories that live deep inside her.
Anaphora, epistrophe, and parallelism occur frequently throughout the rest of the poem. Take a look at lines 6-11:
Working in the hot sun,
And black slaves
Walking in the dewy night,
And black slaves
Singing sorrow songs on the banks of a mighty river
Using anaphora ("Black slaves"/"And black slaves") followed by parallel clauses, these lines create a strong rhythm that evokes both Aunt Sue's "flow[ing]" voice and the "sorrow songs" she's recalling. Lines 12 and 14 then consist of the identical phrase "Mingle themselves softly." This repetition underscores the fact that Aunt Sue is weaving many other stories into her own.
After the epistrophe in lines 1-2, the word "stories" appears again and again at the ends of lines (namely, lines 5, 16, 18, 19, and 25). By landing on this word repeatedly, the poem suggests the way storytelling links the past with the present and future. Aunt Sue is passing on her stories to the "child" (presumably her nephew), who is likely to continue this tradition. In the process, she's passing down important knowledge about her family and culture.
The poem features other kinds of repetition, too. Line 15, for example, contains polyptoton:
In the dark shadows that cross and recross
This effect again suggests the way Aunt Sue's stories weave together the past and present. The "shadows that cross" her stories are the lives of people who are no longer around to relate their experiences. They "recross," perhaps, when they appear in more than one story. Her voice is like a net holding all these experiences together.
Finally, the poem contains a few widely spaced repetitions, such as "Summer nights"/"summer night" in lines 3 and 24, "Listening" in lines 17 and 25, and "brown-faced child"/"dark-faced child" in lines 4, 17, and 23. "Aunt Sue's" name also appears at least once in each stanza. These repetitions heighten the musicality of the language while fixing the poem's setting, action, and characters in the reader's mind.