Solve the puzzles

1. What is black when it's clean and white when it's dirty?
2. What falls but never gets hurt?
3. What doesn't ask questions but needs to be answered?
4. What kind of dog has no tail?
5. What travels around the world but always stays in the corner
6. What has teeth but can't bite?
7. What gets bigger without getting heavier?
8. What goes through the door but never goes in or out?

Answer

1. A blackboard
2. Rain
3. A telephone
4. A hotdog
5. A stamp
6. A comb
7. A hole
8. A keyhole