Answer:
My teeth are sharp, my back is straight, to cut things up it is my fate.
Walk on the living, they don't even mumble. Walk on the dead, they mutter and grumble.
Three little letters. A paradox to some. The worse that it is, the better it becomes.
I'm a god. I'm a planet. I measure heat.
The more of it there is, the less you see.
Iām grown from darkness but shine with a pale light. Very round I am and always a lady's delight.