Yet for many (or even most) species, that is the reality they live with every day. For one gender, sex is the only reason they're alive; for the other, it's a terrifying, painful nightmare. For instance ...

Human beings are kind of lucky in the sense that both genders generally find sex fairly pleasurable. We imagine society would be quite radically different if, say, males thought sex was something to be avoided at all costs.

7 Rhesus Macaque Males Get Attacked Right as They're Climaxing

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For most animals that reproduce sexually, the fun comes with a price. If you're a guy, every so often other guys are going to try to kill you so they can have sex with your girlfriend. It's nothing personal, you're just an obstacle to their mission of spreading their genes around. For communal animals like monkeys, if you're going steady with a lady, you'd best watch your back.

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"Guess where this banana goes."

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But the rhesus macaque takes male rivalry to incredibly dickish new levels. Imagine, if you will, that you're a dominant male macaque and you've just won a fight over the affections of a lady monkey. You take your well-earned reward right there in front of everyone, but just as you reach your climax and throw up your o-face, suddenly you have some shrieking monkey asshole all over you, clawing at your eyes and biting your neck.

That's right, these monkeys have learned that the best time to attack a strong opponent is when he's at his most vulnerable: right at the point of orgasm.

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The rhesus macaque's o-face is one of constant vigilance.

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And this isn't just some hilarious coincidence some scientists saw once -- over half of all macaque sexual encounters end this way. Every time they start to get really into it, they know in the back of their monkey minds that they're putting a "beat the crap out of me" sign on their backs.

How do the sexing males keep falling for this? Apparently, the macaques have also mastered the art of bullshitting. According to researchers, a rival will sneak up to the coupling pair and "feign indifference by digging casually in the sand or pretending to collect handfuls of pebbles" until the moment is right.