Do you see a young woman or an old woman?
This is a famous perceptual illusion in which the brain switches between seeing a young girl and an old woman. Earliest original image is from a German postcard done in 1888. Another example is this advertisement for the Anchor Buggy Company from 1890. The old woman's eye is the young woman's ear. The old woman's wart is the young woman's nose, and the old womans nose is the young woman's chin.