I'm white, and used for cutting and grinding. When I'm damaged, humans usually remove me or fill me. For most animals I am a useful tool. What am I?
I have a little house in which I live all alone. It has no doors or windows, and if I want to go out I must break through the wall. What am I?
There is an ancient invention still used in some parts of the world today that allows people to see through walls. What is it?
