A Yo-Yo ball is this little rubber thing on a rubber string thing with a little hole at the end for your finger. The ball part is filled with water. You use it like a yo-yo, throwing it down and it coming back up to you.
Anyway, I asked if I could play with it for a little bit. He let me hold it and I started throwing it around. It was pretty fun, actually... However, after a few flings, it flew out of my hand and into the street. I went to get it, but a car was coming, and I didn't want to get hit. The car ran over it! I was expecting it to go "POP!" and have water flying everywhere. But it DIDN'T! It just reverted to its normal state. I was about to get it again and another car came and ran over it AGAIN! And it was STILL fine! I finally got it, but I was amazed!
These things are quite durable! They can withstand at least 2 cars running over them! Buy them!