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Pubic lice (crabs) are usually spread through sexual contact. You cannot catch them by using a public toilet.
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.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
Blood is approximately twice as thick as water because of the cells and other components found in it.