The mating ritual of leopard slugs is beautifully bizarre. Each individual has both male and female sex organs — and although they can fertilize themselves, they seem to prefer coupling. Under the cover of night, they climb up a tree or rock or fence post and then lower themselves on a mucus tether, entwining their bodies. Why hang upside-down? Because gravity helps the slugs lower their oversized penises, which emerge through an opening on the right side of their heads. Coitus complete, both sn