Of course, we expect horrifying behavior like this from spiders, but sea slugs? Yes, some of our slimy underwater friends—like the Chromodoris reticulata—appear to have no use for their genitals after sex, either. Most sea slugs are hermaphrodites, and can impregnate each other simultaneously—they may be the most efficient procreators. Researchers in Japan noticed that after the deed was done, the sea slugs would drag their penises around with them for a bit, and then "dispose" of them. Again, the question is: whhhyyyyyy? On closer inspection, scientists found the ends of the sea slugs' members were dotted with small, backwards spikes tangled with sperm. Since sea slug "vaginas" have two separate sperm storage areas, scientists suggested that the barbs on the penises rake out any competitors' sperm. After that's done the penis can't be used again, and like a disposable needle, it's safely discarded of. But don't worry: these sea slugs have two backup penises ready and waiting.