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 adult human brain weighs about 3 pounds (1,300-1,400 g).
99
It takes about 20 seconds for a red blood cell to circle the whole body.
102
One human hair can support 3 ounces.
191
Your thumb is about the same size as your nose.
124
The human body contains over a billion miles of DNA.
147
The largest cell in the human body is the female egg and the smallest is the male sperm.
682