This puzzle was invented by Douglas A. Engel and it consisted of two intersecting discs in a plastic holder.
In the middle of the screen there is the actual playing area. It consists of two circular discs that are intersecting each other. On each disc, there are six stones alternating with six bones. The stones look like overweight triangles, the bones as malnourished rectangles.
Since the discs are intersecting, they share two stones and a bone. If a disc, let's say the upper one, is rotated by 60 degrees, then one stone and one bone that had previously also belonged to the lower disc are replaced by a new stone and new bone.