The "Devil's Balls" of ancient Chinese masters were intricate metal sculptures composed of several interlocking spheres. Inside each sphere is an additional 5 to 20 other balls, unconnected and free-moving. Each one is covered with a delicate engraving that never repeats itself. Masters created them by drilling conical holes in perfect spheres at certain locations, converging exactly in the center; then they marked out future balls with a ruler before cutting them from the center using bent chisels – relying only on their intuition and experience since they couldn't see the surface themselves.