Pop-up example of Professor Sugihara’s ambiguous tube

Professor Kokichi Sugihara of Japan has developed a number of illusions such as this one. When viewed from one direction you see a round tube. When you turn the tube around by 180 degrees, it now appears circular. The effect is even more startling if you place a mirror behind the tube, so you can see both views at once. This pop-up version of the illusion was a gift presented by Michael Colley to attendees of the John Salisse Luncheon Club in London on 23 December 2024.