Answer:
how many words are in those books
What I am filled, I can point the way. When I am empty. Nothing moves me. I have two skins. One without and one within.
What has two legs but doesn't walk?
I don't think or eat or slumber. Or move around or fear thunder. Just like you I look the same but I can't harm you or be your bane.
It's equally comfortable in an orchestra and a geometry textbook. What is it?
What an fill a room but takes up no space?
Difficult
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?