What is the effect of the speaker not completing the final line with a simile and why is this a useful strategy in "Harlem"?

In the eight lines enclosed within the frame (that is,
between the first andnext-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.” By the way, the third ofthese,
“crust up and sugar over—like a syrupy sweet,” probably describes adream that has turned
into smiling Uncle Tomism. Similes can be effective, andthese are effective, but in the
final line Hughes states the last possibility (“Ordoes 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 istoo 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.