Kokichi Sugihara. “Facing-Right Illusion”. Meiji University. Japan
The object appears to be a bird facing right. Even though we rotate it around a vertical axis by 180 degrees, we cannot make it to face left; it turns to the right again. The object is made of hard material, but it appears as if it is deforming continuously during rotation. Mathematically a line-symmetric structure in a 3D space is invariant to 180-degree rotation around the line of symmetry. The object is designed using this mathematical property together with the human preference of a familiar silhouette to an actual 3D shape.