Though they have a simple design and shape, the Black Duo Balls give you effective and amazing internal stimulation. Inserting and removing is easy as both beads have a smooth exterior and are connected to each other by a sturdy nylon cord. The secret to these beads comes after you insert them, as you will start to feel vibrations as you move around. These vibrations are caused by two additional balls located inside each of the beads. When you move, you will cause the balls to roll around, creating vibrations. When done, you can remove them by pulling on the nylon loop located at the end.