Slugs are hermaphrodites (each individual possessing both male and female reproductive organs) so, when reproducing, any two slugs can entwine in a slug ballet. The ballet involves the slugs finding a nice plant twig or leaf and forming a thick mucous which the slugs then suspend themselves from to dangle mid-air. You heard it here first, slugs make little mucous-based fuck swings. How cute is that?
Once they're well entwined, the slugs’ male appendages appear from behind their heads (yes, they’re both dickheads) and entwine. Sperm is exchanged and each slug is left up the duff by the other. Ahhh, so romantic.