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Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
There are 20 feet of blood vessels in each square inch of human skin.
If all the neurons in the human body were lined up, they would stretch more than 600 miles.
If you could remove all of your skin, it would weigh up to 5 pounds.
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.