Banana slugs are hermaphrodites, meaning they have both man and woman parts, and during mating, once the deed is done, they try to bit off each other’s penises, because that’s just the kind of kinky shit banana slugs are into.
Banana slugs begin their mating with a few vicious love nips. Then the animals curl around each other, forming a bright yellow yin-yang symbol. Next, they insert their penises. (Remember, they both have one.) In some cases, one slug provides sperm and the other slug receives it. More often, the slugs swap sperm. Copulation can last many hours. Then, in most cases, the slugs withdraw and part ways.

But not always....