Answer:
You need a key to receive an answer from me. The answer you'll find is straight from your mind. What is it?
I am round as a bowl, deep as a tub, but all the world's water couldn't fill me up.
What can you catch but not throw?
I walked and walked and at last I got it. I didn't want it. So I stopped and looked for it. When I found it, I threw it away.
I weaken all men for hours each day. I show you strange visions while you are away. I take you by night, by day take you back. None suffer to have me, but do from my lack.
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?