Cracking your knuckles does not actually hurt your bones or cause arthritis. The sound you hear is just gas bubbles bursting.
18
After age 30, the brain begins to lose about 50,000 neurons per day - shrinking the brain .25% each year.
55
For most people, no matter how hard you pinch the skin on your elbow with your fingers it doesn't hurt.
515
Enamel is hardest substance in the human body.
61
The average person's skin weighs twice as much as their brain.
131
It takes about 20 seconds for a red blood cell to circle the whole body.
102
It takes twice as long to lose new muscle if you stop working out than it did to gain it.
127
The adult human brain weighs about 3 pounds (1,300-1,400 g).
99