For most people, no matter how hard you pinch the skin on your elbow with your fingers it doesn't hurt.
515
If Earth's life was compressed into 1 year, then humans would have been around for only 2 seconds.
15
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
Shark corneas are used in eye transplants and shark bone marrow can be used to graft human bones.
132
The adult human brain weighs about 3 pounds (1,300-1,400 g).
99
After age 30, the brain shrinks a quarter of a percent (0.25%) in mass each year.
139
Pain occurs when sounds are above 130 db.
124