Science can’t explain everybody structure or function — at least not yet anyway. There are some things your body does that don’t necessarily make sense — like yawning, blushing, and even kissing. But that’s what makes the human body so intriguing.

1. Hypnic Jerks

When you’re falling asleep, you feel like you’re falling off of a cliff, and you suddenly jerk to stay awake, you’re experiencing what’s called a hypnic jerk. The National Sleep Foundation says up to 70 percent of people experience hypnic jerks, but science can’t really explain why this occurs. It could be your body’s way of protecting itself from injury when falling asleep sitting up, but your guess is as good as any to how and why this phenomenon occurs.

2. Sun Sneezing

Autosomal Dominant Compelling Helioopthalmic Outburst (ACHOO) Syndrome, also known as sun sneezing or photic sneezing, is when you begin sneezing in response to sudden exposure to a bright light (like sunlight). The National Center for Biotechnology Information says that while one in four people may sneeze in response to sudden sunlight exposure, the cause of this weird body function isn’t entirely understood.

3. The Placebo Effect

Ever feel like the medical treatment or medication you’ve received is working wonders, only to find out your treatment is actually just a sugar pill? This is an example of the placebo effect in full force. Harvard Health Publications says science can’t fully explain why the placebo effect works, but that the brain’s power of believing (even when something isn’t really happening) is a real phenomenon.

4. Contagious Yawning

Do you yawn in response to someone else’s yawn (or seeing a yawn on television)? This is called contagious yawning and it isn’t just a myth. A 2016 issue of Psychology Today says that study participants yawn more than half of the time when watching videos of yawns and that contagious yawning even occurs between humans and animals (like humans and dogs, for example). Why does this bodily function happen? Scientists don’t really know for sure.

5. Dreaming

You’ve probably wondered why you dream, and what hidden messages (if any) your dreams may reveal. A 2015 issue of Psychology Today says that while numerous theories exist for explaining why and how we dream, no one really knows the purpose (or meanings) of dreams — at least not yet.

6. Blushing

Have you ever suddenly experienced a bright red face for no apparent reason? While blushing is a fairly common phenomenon, it’s not entirely clear how or why our cheeks turn red in certain situations. The Social Anxiety Institute says blushing can occur in people with social anxiety disorder — or in situations where you’re feeling embarrassed or the center of attention in large groups. Even just thinking about blushing can sometimes make your cheeks pink. It’s not entirely clear why the human body does this, but the Social Anxiety Institute says finding ways to reduce anxiety may help lower your risk for blushing.

7. Fingerprints

All humans possess a unique pattern of fingerprints; even identical twins have different sets of prints. This makes it easier to identify people and catch criminals, but the following question remains: why do fingerprints exist? While scientists theorize that these tiny lines and ridges on your fingers may enhance the sense of touch, no one knows exactly why fingerprints are on fingertips (and what purpose they serve).

8. Kissing

Have you ever wondered what the purpose of kissing is? Psychology Today says some cultures don’t kiss romantically at all, kissing may be a learned behavior, and kissing isn’t one of life’s necessities. Whether or not you’re a kisser and who you’re attracted to isn’t really explained by science. A 2014 study published in Evolutionary Psychology says romantic kissing can affect the desire for sex, so these two forms of affection seem to be related.

9. Being Left Handed

Lefties favor left hands for writing, eating, cleaning, working, playing sports, and pretty much any other major life task. Why are some people left-handed, while most people favor their right hands? We don’t really know the answer. The American Psychological Association says about 90 percent of people are classified as right-handed, while the remaining 10 percent are lefties (or are ambidextrous). Why this occurs is anybody’s guess.

10. Body Hair

They mystery of body hair is a puzzling one, especially when it comes to pubic hair, facial hair for men, and even toe hair. Body hair helps regulate body temperature and protects your nose, ears, and eyes from air particles, according to MedlinePlus. But why body hair grows more heavily in men (than women) and on certain areas of the body doesn’t always make sense scientifically.

While science can’t explain everything your body does, theories do exist. In time we may have better answers — but for now some parts of the body still remain a mystery.

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