25 Most Unsettling Facts About the Human Body You Won’t Forget

Disclaimer: Some of the responses below include discussions of human anatomy that may be disturbing for some readers.

1. “Some people have three or more kidneys. When a kidney is transplanted, the old ones often remain unless removal is necessary.”

2. “Your brain can’t feel pain. This explains why surgeries can occur while patients are awake. Pain is sensed by the skin and skull, but the brain itself doesn’t experience it. It’s a bit unsettling when you think about it.”

3. “When you twist your wrist, the bones in your forearm overlap. It’s totally normal biomechanically, although pretty gross if you see a simulation.”

4. “The ovaries aren’t directly connected to the fallopian tubes. Eggs are released into them, not passed through a direct path. Some things can end up floating around in the abdominal cavity. Yikes.”

5. “After surgery, your intestines are simply placed back in. They’ll find their way back to the right position on their own.”

6. “Only about 5% of our brain activity is conscious; 95% is unconscious. What’s creepy is that the unconscious mind often makes decisions before the conscious one is aware, and then justifies them afterward.”

7. “You can technically poop through your mouth.”

8. “Colostomies can contract STDs. Yes, in the way you think.”

9. “Amniotic fluid is essentially fetal urine. They drink it, excrete it, and then drink it again.

10. “Tiny eight-legged mites called Demodex live in and around our eyebrows. They’re actually related to spiders.”

11. “Ribs can regrow. If a small piece is left behind after a medical removal, it can start developing new bone.”

12. “Your pinky fingers are crucial; you lose about 33% of your grip strength without them.”

13. “You can be internally decapitated. The neck can break, leaving your head connected only by soft tissue.”

14. “A teratoma can grow hair, teeth, and tissue, like a body trying to form in the wrong place. This happens when stem cells don’t stop differentiating.”

15. “Some people are born with their organ asymmetries reversed. It’s not creepy until a doctor tries to diagnose appendicitis.”

16. “Dehydration can cause headaches because your brain slightly shrinks.”

17. “Sometimes after a nose injury, a watery fluid (not snot) may leak from the nose. This can be cerebrospinal fluid, which could lead to serious issues like meningitis.”

18. “Your bladder is linked to your belly button. A condition can cause urine to leak from your belly button.”

19. “In rare cases, a fertilized egg can turn into cancer instead of a normal pregnancy. This condition is called choriocarcinoma.”

20. “Endometriosis can appear anywhere in a woman’s body. Just removing the ovaries doesn’t stop the tissue from producing hormones.”

21. “Kids have their adult teeth positioned right above their baby teeth. It’s quite a sight when you see a child’s skull!”

22. “Your retina is an immune-privileged area, meaning if it’s exposed to the immune system, it could trigger attacks that result in blindness.”

23. “A woman’s immune system can occasionally reject a man’s sperm, making conception with that partner challenging, even if both are otherwise fertile.”

24. “Well, that’s quite enough internet for today. I’d happily erase several of these facts from my memory. What’s the one that surprised you the most?”

Text has been edited for length and clarity.