Answer:
I fly through the air on small feathered wings, seeking out life and destroying all things.
What bird can lift the heaviest weight?
This is needed both for courage and hardcover books.
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.
I can be cracked, I can be made. I can be told, I can be played.
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?