Answer:
Turns us on our backs, and open up our stomachs. You will be the wisest of men though at start a lummox.
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 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.
It holds no blessings in disguise. Its rhymes are aimed at your demise, it's cast only to ruin, Whatever you are doin'.
Jack and Jill when up the hill jack fell down
You use it between your head and your toes, the more it works the thinner it grows.
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?