Why does the Termesphere seem to flip and read like it was a concave surface and the motion reverse? My opinion is this: all illusions work because the mind is used to one thing and the designer or artist pushes the image away from that normality. The illusion happens when the mind pushes it back to what it thinks is normal. With the Termesphere, your mind wants to be on the inside of this image to have it be normal. The normal visual world around us is, to our minds, concave. Our minds will push the sphere image, convex, back from the outside of the sphere to the inside, concave. The realism is important for this illusion to happen because we feel like we are more in a normal world with realism. The abstract or geometrically painted spheres can just be that, paint on a sphere. Why is the faster motion important? That is a little harder for me but I think it has to do with you being able to pull the total image together and not think of it as pieces of pictures. When it is all one scene, we know that it is like the world that is always outside of us and we know that scene is on the concave.