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The human body produces and destroys 15 million blood cells every second.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
In the United States, there is a birth every 8 seconds, according to the U.S. Census Bureau's Population Clock.
There are more nerve cells in one human brain than there are stars in the Milky Way.
Although the Roman numeral for the number 4 has always been taught to have been "IV," according to historians, the ancient Romans probably used "IIII" most of the time. This is partially backed up by the fact that early grandfather clocks displayed IIII for the number 4 instead of IV. Early clockmakers apparently thought that the IIII balanced out the VIII (used for the number 8) on the clock face and that it just looked better.