I think that means the mouth shows subtleties of anger and rage b/c of racism and we smile with “torn and bleeding hearts” to cover up our anger.

2 and 3.) We sing but oh the clay is vile/Beneath our feet and long the mile

I think he is saying that although we sing through our unhappiness over African American struggles, we still have a long way to walk. The earth beneath us maybe symbolizes the vile treatment that we “walk through”.

I think he sees the world as being ignorant to the Black struggle b/c “we wear the mask” so well.

RE:
What does he mean?
What does Paul Laurence Dunbar mean when he says:

1) And mouth with myriad subtleties.

2)We sing, but oh the clay is vile

3)Beneath our feet, and long the mile;

This is the poem

WE wear the mask that grins and lies,

It hides our cheeks and shades our eyes,—

This debt we pay…

mean o no? that´s the question