Like many illusions of love, it's obvious once you see it.
The face in the Venetian mask above is not actually one face.
This optical illusion was one of the winners of the Neural Correlate Society's 2011 Illusion of the Year contest. When you look at it, you probably see a face, and don't notice that the blurry photograph is actually that of a man and a woman about to kiss.
When you see two faces, your perception of the photo will flip between two faces and a single face, in what's called a "bistable illusion."
Top 10 finalists in the 2011 Contest, Best Illusion of the Year>>