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.
Right next to the playing area there are four buttons arranged with little arrows on it. With these buttons,
the two discs may be rotated. The rotations can also be initiated with an intuitive finger gesture. This requires a touch on the appropriate disc and then a move in the direction of the desired turn. When the screen is released, the rotation will be executed.
There are 10 Levels and in each level the number of colors will be increased. In the lower levels there is only one color on the stones and bones. Highler levels have multicolor stones and bones.