If you are not comfortable with sex talk or actual photos of that subject run away now.............
Last night I went out to feed the dog and found this business happening on the wall above his bed. I have only seen this once before and that pair were hanging from a branch of a tree. I think the most fascinating bit is that the genitalia comes out of the side of their heads, very very strange!
I'll let Wiki give you a proper explanation of what is going on here!!
'Slugs are hermaphrodites, having both female and male reproductive organs.
Once a slug has located a mate, they encircle each other and sperm is exchanged through their protruded genitalia. A few days later the slugs lay around 30 eggs in a hole in the ground, or beneath the cover of an object such as a fallen log.
Apophallation is a commonly seen practice among many slugs. In apophallating species, the penis curls like a corkscrew and during mating often becomes entangled in the mate's genitalia. Apophallation allows the slugs to separate themselves by one or both of the slugs chewing off the other's penis. Once its penis has been removed, the slug is still able to mate using only the female parts of its reproductive system.' http://en.wikipedia.org/wiki/Slug