Answer:
What lies in a tunnel of darkness. That can only attack when pulled back?
What I am filled, I can point the way. When I am empty. Nothing moves me. I have two skins. One without and one within.
A slow, solemn square-dance of warriors feinting. One by one they fall, warriors fainting, thirty-two on sixty-four.
A tiny bead, like fragile glass, strung along a cord of grass.
Of these things - I have two. One for me - and one for you. And when you ask about the price, I simply smile and nod twice.
I have two eyes in the front and a lot of eyes on my tail