6. Stare at the moon long enough, and the stars should begin to fade away. How many can you get to disappear?
7. Count how many colors you see here. Most people see four: green, blue, and two shades of a pinkish color.
8. As the small circles intersect with the large ones, we seem to see the outlines of a growing and shrinking square. But there is no "square" -- your brain is trying to visualize in terms of solid shapes, and fills in the blanks.