Answer:
Until I am measured I am not known, Yet how you miss me when I have flown.
The more you take, the more you leave behind.
Walk on the living, they don’t even mumble, Walk on the dead, they mutter and grumble. What are they?
Only one color, but not one size. Stuck at the bottom, yet easily flies. Present in sun, but not in rain. Doing no harm, and feeling no pain.
I am mother and father, but never birth or nurse. I'm rarely still, but I never wander.
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?