Answer:
A leathery snake, with a stinging bite. I'll stay coiled up, unless I must fight.
My head bobs lazily in the sun. You think I'm cute. For my face is yellow my hair is white and my body is green.
What is it that no man ever yet did see, which never was, but always is to be?
I bind it and it walks. I loose it and it stops.
I can be written, I can be spoken, I can be exposed, I can be broken.
Black we are and much admired. Many seek us if they are tired. We tire the horse, and comfort man, and turn White when we've fulfilled your plan.