Can you see the younger couple within the older couple, either side of the vase?
The viewer (test person) sees a picture representing a Venetian mask and is asked if he/she notices something special in it. A surprising number don’t notice that the main features of the mask are actually composed of two distinct faces: a man and a woman kissing one another.
Compare the upside-down face on the left of the lower figure with the upright face on the right. The upside-down version looks much thinner, – altogether a longer shaped face than the upright version. Of course the pictures are identical. This illusion illustrates the internal features of the face, (eyes, nose, mouth) can distort our perception of face shape.
Kate Winslet in a stunning optical illusion dress.