There is NOTHING special inside one. It is an illusion as explained in this copy of an advertisement for the ball. " used in the mysterious art of contact juggling. With FUSHIGI the operator exploits the reflective properties of a sphere through specific hand and body isolations and movements that are designed to give the appearance that the FUSHIGI sphere is moving on its own or even floating. The art of maneuvering a reflective sphere through mind and body isolation and manipulation creates the illusion that the sphere may be defying the laws of gravity, as if the sphere is moving on its own." The italicized words should give you an indication of what's going on. It's just another magic trick that when performed looks like real magic.