The animal kingdom features a wide variety of penises that vary in shape, size, and function. Slugakova/iStock via Getty ImagesLeopard slugs have penises that come out of their heads, and since they are hermaphroditic, both slugs can bear offspring when a pair mates. According to limacologists (an amazing word for scientists who study slugs), leopard slugs mate by hanging upside down and wrapping their gooey penises around each other. SnakeТаисья Корчак/iStock via Getty ImagesLike a good s'mores poker, snake penises have two prongs. Known as a hemipenis, scientists have speculated that snake penises developed in a double-branched way due to the location of their cloaca, which is at the base of the tail.