What's on the inside?

My son Brady is the most inquisitive kid I know. And the question he asks most is "What's on the inside of _______?"

After a trip to Discovery Place he was able to have some of his questions answered. We got to see what the inside of the heart, the brain, bones, and the planet Earth looks like. He is now asking questions about things like mushrooms, rocks, and dirt. Our usual answer is , "just more dirt", or "just more mushroom".

His most resent question had us trying desperately not to laugh and hurt his feelings. "What is on the inside of testicles?" Our answer...."just more testicles!!!"