Polysyndeton refers to using several conjunctions in a row to achieve a dramatic effect. That can be seen in this sentence about the child:
The child used to scream for help at night, and cry a good deal, but now it only makes a kind of whining, "eh-haa, eh-haa," and it speaks less and less often.
Comparing this long string of clauses to the ones above it show a much longer sentence structure. It is at this point that the child is dehumanized, moving from actual speech in the sentences prior to losing the ability to communicate due to lack of human stimulation. Therefore, polysyndeton is used to mimic this loss of semantic control as language devolves in structure as well.
Imagery is used to show the contrasting lives between the citizens of Omelas and the child held captive. Consider the following imagery used to describe the processions:
A marvelous smell of cooking goes forth from the red and blue tents of the provisioners. The faces of small children are amiably sticky; in the benign...
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