Cracking your knuckles does not actually hurt your bones or cause arthritis. The sound you hear is just gas bubbles bursting.
18
It takes twice as long to lose new muscle if you stop working out than it did to gain it.
127
Your body is creating and killing about 2.4 million red blood cells per second.
17
Every year your body replaces 98% of your atoms.
119
An average heart beats 100,000 times a day, pumping some 2,000 gallons of blood through its chambers. Over a 70-year life span, that adds up to more than 2.5 billion heartbeats.
73
If your DNA was stretched out it would reach to the moon 6,000 times.
256
The adult human brain weighs about 3 pounds (1,300-1,400 g).
99