Cracking your knuckles does not actually hurt your bones or cause arthritis. The sound you hear is just gas bubbles bursting.
18
Every year your body replaces 98% of your atoms.
119
Your body is creating and killing about 2.4 million red blood cells per second.
17
Poor eyesight (myopia) is associated with higher IQ.
232
For most people, no matter how hard you pinch the skin on your elbow with your fingers it doesn't hurt.
515
Your heart will pump about 212 million liters in its lifetime.
26
Staying awake for 17 hours is the same for your body as drinking 2 glasses of wine.
193
Coughing can cause air to move through your windpipe faster than the speed of sound - over a thousand feet per second!
197