The adult human brain weighs about 3 pounds (1,300-1,400 g).
99
Cracking your knuckles does not actually hurt your bones or cause arthritis. The sound you hear is just gas bubbles bursting.
18
The human brain doesn't stop developing until about 25 years old.
102
It takes twice as long to lose new muscle if you stop working out than it did to gain it.
127
It takes about 20 seconds for a red blood cell to circle the whole body.
102
For most people, no matter how hard you pinch the skin on your elbow with your fingers it doesn't hurt.
515
Your body is creating and killing about 2.4 million red blood cells per second.
17
Yawns are more contagious among people with closer relationships.
163