The Loser Pig

Description:
It's a piggy that can gain weight by filling its tummy with air and lose weight by running and farting. You can blow up its tummy through its nose and let the air out through its back. It whistles when air is coming out from its back and it'll dash forward.

First, you shut the tail valve and blow up the balloon through the nose. Then you shut the nose valve and put it on a flat surface. Open the tail valve; the air comes out from the tail and forces the pig to glide forward.

Principle:
It's based on the principle of action-and-reaction, thrust and pressure. The idea comes from a balloon rocket.

Details:
There is a wheel under each of its legs. There are two valving system: one each for the air inlet and outlet. Since the valves are relatively complicated, they will be more costly to make. The balloon may be loosen over time. But it should be quite durable if operated correctly. This is recommended for kids of age 8 or above, because of the slightly complicated procedure and the necessary lung capacity to blow up the balloon.