When an arm gets severed (which the octopus can regrow), it hangs around for a bit, doing stuff, trying to feed a non-existent mouth. Kinda sad tbh.

Also, male octopuses have a special arm they use for mating. In some species, do avoid sexual cannibalism, they have developed a strategy of ripping it off, upon which it swims on its own towards the female to impregnate her. We live in a world where there are sentient penises swimming around and seeking to mate.