"Love At First Sight" by Alan Ziegler

It was a novelty-store and he went in just for the novelty
of it. She was in front of the counter, listening to the old
proprietor say: "I have here one of those illusion paintings,
a rare one. You either see a beautiful couple making love,
or a skull. They say this one was used by Freud himself on
his patients—if at first sight you see the couple, then you are
a lover of life and love. But if you focus on the skull first,
you're closely involved with death, and there's not much hope for you."
With that, the proprietor unwrapped the painting. They both hesitated, looked at the picture, then at each other. They both saw the skull. And have been together ever since.