Apophallation is a technique resorted to by some species of air-breathing land slugs such as Limax maximus and Ariolimax spp. In these species of hermaphroditic terrestrial gastropod mollusks, after mating, if the slugs cannot successfully separate, a deliberate amputating of the penis takes place.
The slugs are hermaphroditic and have a full set of organs of both sexes. They have relatively large penises which, during mating, wrap around each other in a tight spiral. They sometimes have difficulty separating afterwards. When separating seems impossible, one slug gnaws off either its own, or its partner's penis, so that separation is then possible. No replacement penis grows, and the apophallated slug adopts a purely female function from that point onward.
(We've been having a pretty heavy slug infestation due to the inordinate amount of rainfall we've been getting...luckily, they don't seem to like pineapple)
As if that wasn't fascinating enough, their sex organs protrude from the side of their head.
And if that didn't boggle your mind, how about eating slugs (warning: cute and gag inducing at the same time)?