When your body breaks down food, nearly all the colorful pigments are removed, leaving behind only a grayish mush. However, as your body recycles old red blood cells (which it does every day), some of the leftover material is sent to your small intestine to be digested along with your food. That digestion leaves behind a chemical called stercobilin, which is brown. Your body has no use for stercobilin, so it gets rid of it along with the rest of the waste - coloring your poop brown!

Tears are salty for the same reason sweat and blood are salty - because your body is salty! Every cell in your body maintains a small amount of saltiness in order to work properly. That amount is about 1 part salt for every 100 parts water, or about ⅓ the saltiness of sea water. That’s salty enough to taste - which is why your tears taste salty.

Scientists still aren’t 100% sure why we yawn, but the leading theory is that we yawn to cool down our brains. Yawning takes in lots of air past the backs of our throats, where there’s a major artery carrying blood to our brain. The passage of air could cool that blood down, helping to maintain our brain’s temperature when it starts to overheat. And your body temperature rises just before bed, which might be why you yawn when you’re tired!

Eyes are one of the only parts of your body that never grow. Past 3 months old, your eyes don’t get any larger. That’s why babies seem to have such big eyes - their eyes are the same size as an adults, even though their heads are much smaller!

Earwax (or cerumen, if you want to be scientific) is made just inside your ear, past where you can safely reach. Once produced, it slowly moves to your outer ear (the part of the ear you can see). Along the way, it moisturizes the ear canal, fights off infections, and removes any dust particles that enter your ear. Basically, your ear is a hole to the inside of your body, and earwax is what keeps it protected!

Snot (or mucus) is made by your nose to catch dirt and dust particles that go up your nose, before they get into your lungs. When those particles clump up, they get dry and turn into boogers. So, boogers just mean your nose is working properly by catching stuff before it gets any farther into your airway.

We cough to get rid of anything we don’t want in our airway, whether its tiny particles, bacteria-filled mucus (aka snot), or food that went down the wrong pipe. Keeping your airway clear is extremely important - you need to breathe! Because of this, your body immediately and forcefully gets rid of anything it detects that shouldn’t be there, and it does this by coughing.

When the hair on your skin is faintly brushed, your body gives you an itching sensation, prompting you to scratch it. This is your body’s way of protecting your skin from insects, parasites, and other things that could damage it.

If you look at your wrists, you might be able to see bluish blood flowing underneath the skin. Does that mean your blood is actually blue? Or is it only blue when it doesn’t have oxygen? Well, turns out, your blood is never blue - the bluish color is just due to your skin filtering out reddish light. Human blood is regular old red - sometimes bright, sometimes dark, but always red.