The elephants shadow
Smaller than four, yet bigger than three, to make it your food, you must add an E.
What is it?
What costs nothing but is worth everything, weighs nothing, but can last a lifetime, that one person can't own, but two or more can share?
A man takes a barrel that weighs 20 kilos, and then puts something in it. It now weighs less than 20 kilos. What did he put in the barrel?