Airplanes and Houses and Bears...OH MY!!

While having a conversation in the car, Zack asked if Outer Space was bigger than the sky. I told him yes. Then he asked if the space ship was bigger than outer space, and I told him that the space ship (shuttle) goes in outer space. Then I decided to give him an idea of how big the universe is and how small we are comparatively. I told him to picture picking up a handful of sand, the picking out one tiny grain of sand from that handful. If that handful of sand is the universe, then we are the tiny grain of sand. Could be an exaggeration, but it's okay for now: he doesn't really have any concept of time or space. He seemed to understand that, and he was quiet for a few, short seconds. Then he asked me if a space ship was bigger than anything else on Earth. While I pondered that, he said, "Except for airplanes and houses and bears." Bears!?!?