Cracking your knuckles does not actually hurt your bones or cause arthritis. The sound you hear is just gas bubbles bursting.
18
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
The human brain doesn't stop developing until about 25 years old.
102
Yawns are more contagious among people with closer relationships.
163
One human hair can support 3 ounces.
191
Enamel is hardest substance in the human body.
61
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