Analysis of A Rough Sketch

I caught, for a second, across the crowd--
Just for a second, and barely that--
A face, pox-pitted and evil-browed,
Hid in the shade of a slouch-rim'd hat--
With small gray eyes, of a look as keen
As the long, sharp nose that grew between.

And I said: 'Tis a sketch of Nature's own,
Drawn i' the dark o' the moon, I swear,
On a tatter of Fate that the winds have blown
Hither and thither and everywhere--
With its keen little sinister eyes of gray,
And nose like the beak of a bird of prey!