Science Has No Definite Explanation For Morning Wood. The clinical term is "nocturnal penile tumescence." The old "it keeps you from peeing in bed" explanation we've all heard isn't completely true. The theory is plausible, but scientists can't explain why BEMHO (look it up on Urban Dictionary, grandma) comes and goes 3-4 times a night. There is actually no rock-solid explanation for why it occurs. Sorry.
Semen Contains Mood-Elevating Compounds. Contained within semen are chemicals such as serotonin, oxytocin, endorphins, and other mood-elevators. It has been theorized that oral ingestion of semen will introduce these chemicals to the recipient's brain. Science hasn't proven it 100% yet, but your "why she should swallow" argument just got a lot stronger.
Penises Are Shaped To Pull Other Guy's Sperm Out Of The Vagina. Think about evolutionary biology for a minute. Survival of the fittest, right? Your penis knows this, and that shape helps you cancel out women's natural instinct towards promiscuity (it's science, look it up.) The penis' shape creates a slight suction within the vagina, meant to pull other men's semen back out of there. The shape also works like a shovel, making room for your seed.
"Balls Like A Gorilla" is Actually an Insult. True facts: Human testicles are bigger than gorilla testicles. There's not a real way around that fact. Challenge a gorilla to a big balls contest, and you're going to win. But don't get too confident. Chimpanzees have bigger testicles than humans.
The Angle Of Your Erection Varies From Person To Person. Science actually took the time to measure the angle of guys' erections while standing. A healthy erection should point slightly upwards, but never to the side. The exact angle isn't particularly important, however a 60-80 deg angle is most common -- 31% of men point this way. 5% of men have a 0-30 deg erection, 30% point 30-60 deg, 10% from 80-95 deg, 20% from 95-120 deg, and 5% of men point at a baffling 120-180 deg angle.
There Are Sperm That Play Defense. A portion of your sperm is there to get the job done while another portion acts as defenders to kill other guys' sperm. And then there's another portion still that just runs interference--basically just there to lay down a protective layer after they're instantly killed by the hostile environment of the vagina.
Your Scrotum Would Have Been Labia if You Were a Girl. Homology happens when two body parts have a shared ancestry. Basically, your scrotum is made out of the same stuff as labia--they just form into different parts when your sex organs start differentiating in the womb. During the process of sexual differentiation, the cells decided to make a sack instead of lips.
Sperm Show Up With a Backstage Pass. Human sperm are made with a coating of glycoprotein molecules. When they enter the woman's body, this glycoprotein acts as a chemical signal that the sperm are not to be attacked by the woman's immune system. Glycoprotein is sperm's way of saying "It's cool. We mean you no harm! We just want to make you pregnant!"
There's a Pretty Good Chance Frequent Ejaculation Might Prevent Cancer. Two recent studies found that men who ejaculate seven or more times a week were at much less risk for prostate cancer than their unlucky pals who only fired three or less rounds a week. There's no real reason for it, and it's still under further investigation, but you can't be too careful.
A Foot or Two is an Average Ejaculation Distance. Alfred Kinsey measured distance of ejaculation in a few hundred men and determined that 1-2 feet is the average distance they could reach. Some men were able to regularly hit 5-6 feet and apparently a few of the elite could carry the green at about 8 feet. Accuracy was not measured, but that would be a great Sex Olympics event.
There is No Body Part That Indicates Penis Size. Feet, hands, nose, whatever... none of them have anything to do with the size of your junk. Men with big feet wear big shoes--that's it.
Your Scrotum Has Its Own Thermostat. The muscle that contracts the scrotum and draws the testis up to the body is called the Cremaster muscle. Its main function is to raise and lower the testes to keep their temperature steady. When you get scared and they shoot up inside you, that is a protective function.
Testicles Are Almost a Yard Long When Unravelled. Since the testicles are really just a system of ducts and tubes--you really could unravel a testicle. Completely unraveled, the average testicle is 2.5 feet long. Don't tell your girlfriend though, she doesn't need something else to threaten you with.
Premature Ejaculation is Likely Hereditary. If you're often caught coming out of the gates a little early, you may want to ask Dad about that. An awkward medical study found that 91% of men who have struggled with premature ejaculation also had a first relative who did as well.