Before we get to the juicy bits (slimy bits?), you need to know a bit about slug anatomy. Most slugs are simultaneous hermaphrodites and have both a penis and a genital opening, so that when they have sex they both fertilize and are fertilized. (They then both lay eggs somewhere damp and out of the way, and that is it for parental care.) Also, due to the vagaries of evolution, the genitalia and anus of slugs are located on the right side of their heads. This is because slugs are descended from snails with spiraling shells – the snails needed to move their naughty bits down in order to extend outside the shell, so they put them on their head. Even though slugs have since lost their shells, they have retained this feature of snail anatomy. So most gastropods actually poop on their own heads – ain’t nature grand?