Topology is a profound branch of mathematics, but it is also very interesting. It is closely related to topics like knots, paper strips, and untangling wires. There are hundreds of mysterious topological games passed down in Chinese folk culture. Among them, quite a few have been sought after by foreign mathematicians due to their complex structures and ingenious solutions. It is said that the great German mathematician Felix Klein was once an enthusiastic collector of such puzzles. Below, I will introduce a very simple yet fascinating one.