Answer:
It cannot be seen, it weighs nothing, but when put into a barrel, it makes it lighter.
What has one eye but cannot see?
With head without hair. With mouth without tooth.
They have not flesh, nor feathers, nor scales, nor bone. Yet they have fingers and thumbs of their own. What are they?
What can be heard and caught but never seen?
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?