Answer:
Gets rid of bad ones, short and tall. Tightens when used, one size fits all.
Mountains will crumble and temples will fall. And no man can survive its endless call.
Break it and it is better, immediately set and harder to break again.
Lives without a body, hears without ears, speaks without a mouth, to which the air alone gives birth. What is it?
I cost no money to use, or conscious effort to take part of. And as far as you can see, there is nothing to me. But without me, you are dead.
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?