Great for STEM teaching. Unlock some of the coolest science mysteries using physics, center of gravity and more. Balancing Nail Puzzle - To win this challenge, all 11 nails must balance only on the single standing nail. None of the eleven nails may touch the base, the desk or table, or anything else that might help hold them up. Salt and Marble Challenge - The object of the challenge is to move the marble from one end of the test tube to the other, but you'll have to get through all of the salt. Once you uncover the secret, you'll understand how to find the toy surprise in your breakfast cereal without having to dig through the entire box. Balloon in a Bottle - Here's a challenge that seems to be easy until you try it. Inflate a normal balloon inside of a plastic soda bottle. That's easy, right? You'll quickly realize that it's impossible to inflate a balloon inside of a bottle because something invisible inside the bottle is pushing against the balloon. This challenge is all about the properties of air, and it's guaranteed to amaze your friends.