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
Enamel is hardest substance in the human body.
61
The average sperm cell swims at 8 inches per hour.
76
Your heart will pump about 212 million liters in its lifetime.
26
The average person's skin weighs twice as much as their brain.
131
The adult human brain weighs about 3 pounds (1,300-1,400 g).
99
Your thumb is about the same size as your nose.
124