Rubbing your eyes increases the pressure within the eyeball and this pressure activates ganglion cells in the retina in the same way as light does. Your brain doesn’t know the difference and so interprets the activation as though you were seeing light from the world outside.
2. The rarest natural hair color in the world is red, with only 1-2% of the world population having naturally red hair. The second is blond, with 3%, then brown/brunette, with 11%, and finally black with 75-85%.
3. The average human body has enough iron in it to forge a metal nail that is 3-inches long, enough sulfur to kill all fleas on a dog, enough carbon to make 900 pencils, enough potassium to fire a toy cannon, enough fat to make 7 bars of soap, and enough phosphorous to make 2,200 match heads.
4. Humans hear anywhere from 20 to 100 times faster than they see so that everything that they perceive with their ears is coloring every other perception they have and every conscious thought they have. The sound gets in so fast that it modifies all the other input and sets the stage for it.
5. We breathe (mostly) out of only one nostril at a time, alternating (on average) every 2.5 hours. This is controlled via turbinates, which are small structures inside the nose that consist of bony projections covered by erectile tissue, filling one side with blood while shunting blood away in the other.
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A rare mutation among the Bajau people in Southeast Asia lets them stay underwater longer. Natural selection at the PDE10A gene has increased spleen size in the Bajau, providing them with a larger reservoir of oxygenated red blood cells.
7. The 'stomach in your mouth feeling' on a roller-coaster is your organs floating inside you.
8. Whenever you move your eyes quickly from one point to another point, there is a disconnect between your eyes and brain, so your perception of time stretches backward slightly. This is why, when you first look at a clock, it appears to take longer than a second to move.
9. Your heart rate slows when your face touches water. This is called the mammalian diving reflex.
10. One of the reasons your lungs feel refreshed when walking through a pine forest is because of an anti-inflammatory compound called a-Pinene, found in conifers. It is used as a bronchodilator in the treatment of asthma and is abundantly present in marijuana.
11Tensor tympani muscle
Some people can voluntarily cause a rumbling sound in their ears by tensing the tensor tympani muscle.
12. People with sensitive noses are capable of smelling when it's about to rain due to atmospheric chemicals reacting and creating ozone, which has a pungent, sweet smell.
13. There are nerve endings that exist only to recognize a gentle stroking touch. Their activation decreases the heart rate and activates the smile muscle. Their optimal speed is 3-5 cm/s, which means we are genetically wired to cuddle and caress each other at predetermined velocities.
14. Halting sneezing via blocking the nostrils and mouth is a dangerous maneuver. It may lead to numerous complications, such as pneumomediastinum (air trapped in the chest between both lungs), perforation of the tympanic membrane (perforated eardrum), and even cerebral aneurysm.
15. Humans don't actually have five senses, we have other senses like balance, heat, pain, and the passage of time. Humans actually have at least 14 senses.
Rh-null, the rarest blood type of the world, has been called the "Golden Blood". This blood type is so rare that only 43 people in the world have it, and there are only 9 active donors.
17. One person in four is a 'supertaster', who experiences the sensation of tasting more intensely. Supertasters have a high density of taste cells on their tongue but are likely to have a distaste for beer.
18. Low gravity makes it difficult to tell if your bladder is full because the bladder’s stretch receptor nerves don’t feel the weight of the liquid. Astronauts are trained to empty their bladders every two hours because of this.
19. When a healthy person donates a kidney, their other normal kidney will increase in size to compensate for the loss of the donated kidney.
20. The human anus is covered by cells similar to those in our mouths. That’s the reason you can feel the spicy foods down there just as much as in your mouth.
Human hair from hair salons which are rejected by wigmakers are being used to create oil adsorbing booms for ocean oil spills. Human hair can adsorb 3-9 times its own weight in oil.
22. Coughing while cleaning inside your ears is not something that everyone else experiences and is actually an uncommon reaction called Arnold’s Nerve Reflex.
23. You can count to 12 on one hand by using your thumb to count the bones of each finger. This might explain the base 12 and base 60 number systems we use for telling time and measuring angles.
24. The skin of all human beings is covered in stripes. They are called Blaschko’s Lines, and they cover the body from head to toe. We just can't see them.
25. When the liver fails to produce bile your poop doesn't get the regular brown pigments so it becomes white.