24. Baboons (and others)
In certain species, such as baboons, rats, squirrels, bees, scorpions, and spiders, the males are able to inject a sealing type of plug inside the female after mating. In the case of bees, this plug is actually his entire penis, which detaches and stays inside her. For others, like baboons, it’s just a thick gelatinous goo. This plug prevents any other males from mating with her, ensuring it will be his DNA which she passes along to offspring. And you thought an engagement ring was a man’s way of marking his territory! It’s probably a good thing men can’t do this; most of us make questionable mating choices from time to time. No sense in being stuck (pun intended) with him forever.