Center of gravity is the point in a body around which its weight is evenly balanced. If positioned correctly, the forks and potato will be in a state of stable equilibrium and don't fall. The handles of the forks are curved toward the potato, which shifts the heavier portion towards the potato. The center of gravity is directly on the spot where the toothpick rests on the thread. A circus tightrope walker often uses a long stick for balancing in the same way as the forks are used in this experiment.