Answer:
My teeth are sharp, my back is straight, to cut things up it is my fate.
Only two backbones and thousands of ribs.
Man walks over, and man swims under. In times of war, it can be burned asunder. What is it?
In buckles or lace, they help set the pace. The farther you go, the thinner they grow.
You can hold it without using your hands or arms. What is it?
Iām grown from darkness but shine with a pale light. Very round I am and always a lady's delight.