The transfer ball has holes. What is this?

This kind of thing is called exquisite ball, scientific name ghost ball.

Ghost ball, also called concentric ball, or tooth carving ball cover, is a hollow ball carved from wood, ivory or jade. A plurality of hollow concentric circles are nested inside the sphere, and the inner sphere can be rotated by passing a hairpin through the hole of the outer sphere. A few skilled craftsmen can even nest dozens of layers of balls, and each layer can move. It is exquisite and complex, and it is simply breathtaking, so it is called the uncanny workmanship, so it is called the uncanny workmanship ball. According to Cao Zhao's "Gegu Yaolun" in the Ming Dynasty, the practice of ball-trapping had been practiced as early as the Song Dynasty. At that time, craftsmen could already make three-layer nested balls, and at that time, the name "ghost work ball" already existed.

During the Qianlong period, the ghost ball rose again and reached a new peak. At that time, it was incredible that the recorded ghost ball could carve up to 60 layers of nested teeth. However, after the peak of Qianlong dynasty, the ghost ball went downhill. For example, the later emperor Jiaqing was a fan of ghost ball. His collection of a 13-story ivory ghost ball has become a national treasure, but it is no longer comparable to the ghost ball nested in thirty or forty stories during the Qianlong period, not to mention that it is made of ivory, not jade, and its value has been greatly reduced. By the end of Qing Dynasty, the carving technique of Jade Ghost Ball was simply lost. If someone could take out the ghost jade ball at that time, it was really a treasure among treasures, and it was priceless.