Talk about form in either “what the mirror says” or “Harlem” and consider if the form enhances the figurative language used in the poem

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.