Answer:
A dagger thrust at my own heart, dictates the way I'm swayed. Left I stand, and right I yield, to the twisting of the blade.
During the 1800's these turned women into hourglasses and is becoming more popular again these days
I am free for the taking. Through all of your life, though given but once at birth. I am less than nothing in weight, but will fell the strongest of you if held.
What can be seen but never found that only hides in the unwound?
A dragons tooth in a mortals hand, I kill, I maim, I divide the land.
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.