>And what rough beast, its hour come round at last,
Slouches towards Bethlehem to be born?

Geez, when you say slouches like that is sounds really threatening, like something evil is slithering on its way.

Slouches here, is usually done by teenages just hanging loose, not sitting upright, but with their backs curved a little.

Somehow though, your use seems very apt and conveys the "dark brooding shape coming this way" well.