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.
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 ...
7 Rhesus Macaque Males Get Attacked Right as They're Climaxing
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.
"Guess where this banana goes."
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.
The rhesus macaque's o-face is one of constant vigilance.
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.
"Mind if I stand suspiciously near your genitals and just, y'know, chill?"
And it's not always just one attacker -- up to nine monkeys have been known to join the surprise attack, leading to the world's most severe case of monkey blue balls.
Hey, speaking of which ...
6 The Short-Beaked Echidna's Balls Swell Up to 500 Percent While Waiting for Sex
Lots of men suffer anxiety about the power of their equipment. Not so for the short-beaked echidna, which packs a four-headed superpenis. When it engages in sweet echidna loving, only two heads work at any one time while the other two rest, meaning it doesn't need to worry about the 20 or so minutes of downtime that plagues human men.
"Another couple of dicks would come in real handy just now."
Unfortunately, the echidna has a different problem. Short-beaked echidnas are basically solitary animals, and the only time they gather is mating season, from the end of June through the beginning of September. To get ready for this, their testes start swelling with seminal fluid. The bad news is that the testes aren't external, but they stay inside the body. And when we say they swell up, we mean really swell -- to at least 200 percent of their normal size, to be exact.
"Oh, oh God, I can't feel my feet. I can't feel my feet!"
What's more, the ladies they're looking to impress are incredibly picky. So picky, in fact, that they will only have sex with one guy, one time, during the entire mating season. So the male has to follow her around, along with several other guys, while they try to fight their way to the front of the line of suitors.
They have to do all this while dealing with their gigantically, painfully swollen balls, knowing that if they don't get their chance, it will be 10 months before they get to try again.
Currumbin Wildlife Hospital
"Large bundles" of echidna sperm. Their whole mating cycle must be like the first two hours after a trip to P.F. Chang's.