Answer:
How do you discover something that does not exist?
A man goes upstairs to grab his time machine. He walks downstairs then goes back in time 200 years. Why did he go downstairs?
How can you throw a ball 20 meters, and have it come back to you without hitting anything?
What is yours but only used by others?
If there are three apples and you take away two, how many do you have?
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?