Yawns are more contagious among people with closer relationships.
163
The average sperm cell swims at 8 inches per hour.
76
Chewing gum boosts your brain power.
285
It takes about 20 seconds for a red blood cell to circle the whole body.
102
Oxygen, carbon, hydrogen and nitrogen make up 90% of the human body.
118
It takes twice as long to lose new muscle if you stop working out than it did to gain it.
127
Cracking your knuckles does not actually hurt your bones or cause arthritis. The sound you hear is just gas bubbles bursting.
18