Aplysia californica (or the sea hare) are marine mollusks with an unusual reproductive strategy. They are simultaneous hermaphrodites, which means each individual can produce both sperm and eggs. However, they do not self-fertilize and need to mate with different animals to reproduce. When they mate, they frequently form a daisy chain or mating circle with each animal mating as a male at the head end and as a female at the back end. The animal seen in the middle is grinning because it is enjoying the benefits of mating both as a male and a female!