Answer:
You use it between your head and your toes, the more it works the thinner it grows.
What does everyone know how to open but not how to close?
The more you take, the more you leave behind.
Held firmly in the hands, like a sword it cuts deep. Bloodless strokes, all, then forward we leap.
Halo of water, tongue of wood. Skin of stone, long I've stood. My fingers short reach to the sky. Inside my heart men live and die.
I have two eyes in the front and a lot of eyes on my tail
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?