Babies have more bones than adults
You may have heard that a person has 206 bones. That’s sort of true: Most adults have somewhere around that number. You’ll never know exactly how many you have, anyway, since a lot of them are little bitty bones like sesamoids in your finger joints. Babies, though? They have even more. The average baby has about 300 bones. That’s because a lot of things that are one bone in an adult are actually multiple separate bones, joined by cartilage, in little ones. Take the skull, for example: babies’ “soft spot” is just the cartilage in between some of the head bones that haven’t fused together yet.
We glow in the dark, but only slightly
Do you think bioluminescent animals, like anglerfish, are cool? Good news: You glow too, in a similar process called biophoton emission. The chemical reactions in our cells throw off tiny amounts of light that scientists have been able to capture with ultra-sensitive cameras. You can’t see the glow with the naked eye, though—it’s a thousand times weaker than what we can detect.
Your appendix isn’t useless
The appendix, that little wormlike thing that dangles off our large intestine, was once thought to be a mystery, a vestige of something in our evolutionary past. (Rabbits, for example, have a much larger intestinal pouch in that same area, which they use for digestion.)
It turns out that our appendix, far from being a useless lump of flesh, is full of tissues associated with the immune system. The current thinking is that it may serve as a backup storage site for our “good” gut bacteria, the better to replenish them after something like a bout of diarrhea.
Goosebumps are your skin trying to fluff up your body hair to keep you warm
Have you ever seen a bird on a cold day with its feathers all ruffled up so it looks like a little puffball? Or a squirrel, doing much the same thing with its fur? That’s what your body is doing when you get goosebumps: Standing up each of your body hairs to better trap air underneath them to keep you warm.
It doesn’t work very well, of course, since we don’t have that much body hair. But if you look closely, you’ll notice that each goosebump is located at a hair follicle. There is actually a tiny muscle, the arrector pili (literally, “stander-up of hair”) that contracts to pull the hair upright.
You only breathe through one nostril at a time
When you get a cold and have a stuffy nose, you may notice that only one nostril is stuffed up at a time, and which nostril that is changes throughout the day. That’s because we only breathe through one nostril at a time, even when we’re healthy. (The nostril that’s stuffed is just the one that happens to be resting at the moment.)
This is called the nasal cycle, and you can prove it to yourself by putting a hand under your nose. You’ll probably feel your breath more on one side than the other; if you feel it in both, you’ve caught the cycle during its transition. Wait a little while and feel again. I’m breathing through my left nostril right now.
We have invisible stripes
Tiger stripes aren’t just for tigers; human skin has a similar stripey pattern. We just can’t usually see it.
Our stripes, called Blaschko lines, are formed as our cells are dividing and our body is growing in utero. These rows of cells, including skin cells, look identical and are thus not visible as stripes—most of the time. But certain rashes will follow the lines, making them visible, and sometimes they can be seen under powerful-enough ultraviolet light.
Everyone’s pee stinks when you eat asparagus, even if you can’t personally smell it
Does your pee stink after you eat asparagus? This used to be a debated topic, with some people swearing it was true and others having no idea what their neighbors were talking about. It turns out some people smell a cabbagey odor in their own urine, and some don’t, so the next evolution of this weird fact is that some people produce the odor and others don’t.
But there’s yet another layer to this strange fun fact: People who say they don’t get stinky urine also can’t detect the stink in other people’s urine. (That must have been a fun study to conduct.) The current theory is that we all produce the stink, but only some of us can smell it—but scientists still aren’t entirely certain. It’s possible that only some of us make the stink and only some of us can smell it.
Babies only blink once or twice a minute
The average adult blinks 10 to 15 times per minute. But babies don’t: Studies only count them blinking one to three times each minute. We’re not sure why—maybe because they stare at things for longer stretches than grownups do, trying to soak it all in.
Your stomach is constantly digesting itself
If your stomach has so many enzymes and acids that it can digest a piece of meat, why doesn’t it digest itself? Well, it turns out that it kind of does. The cells lining your stomach reproduce quickly to replace the cells that get destroyed in the course of their daily jobs. We end up with a new stomach lining about every three days.
Your DNA is 99.9% identical to a stranger’s
You probably think you’re so different from everyone else, but genetically all humans are extremely similar. Even though you might describe an unrelated person as not sharing any of your DNA, the truth is that all humans have about 99.9% of their DNA in common. All the differences between you and a stranger are in that other 0.1%. While we’re at it, you share about 98.8% of your DNA with a chimp.
Your poop is liquid when it’s inside of you
Skip the diarrhea jokes—you know what I mean. Even though food enters your body as a solid and leaves it (usually) as a solid, it spends most of the time in between as a liquid. Think about it: your stomach is basically an acid bath, and your small intestine is a thin tube, like a garden hose. There’s no solid hamburger making its way down the pipe; food in the process of being digested is a liquid called chyme. Only at the end of your former food’s journey is most of that water absorbed back into the body, leaving solid waste at the end.
You make enough saliva each year to fill a bathtub or two
Our bodies make a lot of, well, stuff. How much? A lot.
You make 0.7 liters of saliva per day, or more than a water bottle’s worth. Over the course of a year you could fill a bathtub or two.
You fart between 15 and 25 times per day, and the total volume can be as much as 1.8 liters—enough to fill a small party balloon.
You make about 1.5 liters of mucus every day, but it’s not all in your nose; mucus also lines other areas of our body, such as our lungs. Most of what gets produced in your nose, by the way? You swallow it.
Gravity makes you shorter
Gravity really is keeping you down. When astronaut Scott Kelly returned from space, he was two inches taller than his twin. Most of us are a tiny bit taller in the morning than we are by the end of the day.
Teeth are not bones
As funny as it is to joke about our teeth as “outside bones” or “luxury bones” (since you have to pay extra to insure and care for them, which I agree is bullshit), teeth are actually not bones at all.
What are they, then? They’re teeth! They’re their own thing. Teeth have a coating called enamel (the hardest substance in the human body), are made of dentin underneath, and have a pulp full of nerves and blood vessels on the inside. Bones, by contrast, have fatty marrow and/or something called “spongy bone” on the inside, and the outside of the bone is coated in a membrane. Bone is full of collagen and blood vessels; the hard parts of teeth have neither.