You might know a lot about sex, but you don't know everything. In my years of sex research, I've kept a list of the most startling and bizarre sex facts I've ever come across. Below are 20 of my favorite weird truths that I found on the internet about sex that are guaranteed to either turn you on, gross you out, or at least give you a serious sexual reality check.

1. Over the course of two weeks, a single human male produces enough sperm to impregnate every fertile woman on the planet.

2. Your worst fear is a reality: the penis gradually shrinks with age.

3. A quick kiss burns about 2-3 calories, whereas more passionate kiss burns 5 or more calories, depending on the duration and intensity.

4. Masturbation has a lot of health benefits! For example, it's good for stress management, it's good for your pelvic muscles, it releases endorphins, it lowers the risk of type-2 diabetes and of prostate cancer, it reduces depressions, it prevents cervical infections in women, and it helps you fall asleep!

5. Also, masturbating is one of the most effective natural ways to cure period cramps.

6. Eating semen can make you less depressed! Or, at least it's packed full of natural mood-enhancers, like. prolactin, oxytocin, serotonin and estrone, which are natural antidepressants.

7. The word "vagina" comes from the Latin root meaning "sheath for a sword."

8. Seventy-five percent of Malawians believe that homosexuality is a "Western invention."

9. Roughly half of Americans lose their virginity by the age of 17, but 10% stay virgins after the age of 24.

10. One in ten European babies is conceived in an IKEA bed.

11. Forty-six percent of Israel's Arab citizens say they would be bothered by having a gay couple as their neighbors.

12. Nine Viagra tablets are sold every second.

13. There is more to the clitoris than the eye can see. The clitoris is actually close to four inches in length, however three fourths of it is inside body. And the clitoris actually grows throughout a woman's life. After menopause it can grow 2.5 times larger than it was during the teenage years.

14. The clitoris has 8,000 nerve endings, which is double the amount of nerve endings in the glans of a penis.

15. 75% of Japanese women own a vibrator, but the average worldwide is only 47%.

16. Most women get more horny than usual right before their period.

17. A woman is more likely to consider committing adultery during ovulation than at any other time in her menstrual cycle.

18. The American Psychiatric Association listed homosexuality as a mental illness until 1973.

19. Some women cum during childbirth.