The applet shows polygons rotating at the vertices of a stationary one. Rotations could be centered at the vertices, or be a little displaced.

It could be observed that sometimes the sides of the stationary polygon appear to be misoriented, like in the first of the two figures above. In the second figure, the stationary shape appears to be circular rather than hexagonal.

Among the stationary figures, the triangle appears the least susceptible to the illusion, while, as the rotating shape, it's the most useful. The original illusion (a hexagon with six small triangles at its vertices) was invented by Italian Walter Gerbino.

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