In the eight lines enclosed within the frame (that is, between the first and next-to-last lines) we get four possibilities: The Dream may “dry up,” “fester,”“crust and sugar over,” or “sag.” Each of these is set forth with a simile,for example, “dry up / like a raisin in the sun.” Similes can be effective, and these are effective, because they are so closely packed together in the form Hughes constructs, but in the final line Hughes states the last possibility (“Or does it explode?”) directly and briefly, without an amplification. The effect is, more or less, to suggest that the fancy (or pretty) talk stops. The explosion is too serious to be treated in a literary way. But, of course, the word “explode,”applied to a dream, is itself figurative. That is, the last line is as “literary” or“poetical” as the earlier lines, but it is a slightly different sort of poetry.A word about the rhymes: notice that although the poem does use rhyme,it does not use a couplet until the last two lines. The effect of the couplet(“load” / “explode”) is that the poem ends with a bang. Of course, when one reads the poem in a book, one sees where the poem ends—though a reader maybe surprised to find the forceful rhyme—but an audience hearing the poem recited is surely taken off-guard. The explosion is unexpected (especially in the context of the two previous lines about a sagging, heavy load) and powerful. The form does reinforce the powerful language used by Hughes.