What to do
Compare the two tables in the neighbouring figure. Which would be easier to get through a narrow door? How do size and shape of the two table tops compare?
Now either press the ‘Run’ button, or click and drag the left table top on top of the right table. If you click & drag far off that parallelogram you can rotate it and test whether it fits.
The two table tops certainly do not look alike!
This phenomenon plays on the interchange of 2- and 3-dimensional interpretation of the figure. If the figure depicted a real-world scene, the real tables certainly would have a different shape.
Roger N. Shepard originated this one among a number of beautiful illusions, which he drew himself; many of which are now “floating around the internet” without proper attribution (e.g., the elephant with the impossible feet), his “Terror Subterra” is also in the present collection. He also invented the “ever rising scale” auditory illusion. The original of the present illusion is called “Turning the Tables”.
Shepard RN (1981) Psychological complementarity. In: Kubovy M & Pomerantz JR (eds) Perceptual organization. 279–342. Hillsdale, NJ: Lawrence Erlbaum Associates
Shepard RN (1990) Mind Sights: Original Visual Illusions, Ambiguities, and other Anomalies, New York: WH Freeman and Company