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Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
The Babylonians wrote numbers in a system that used 60 as the base value rather than the number 10. They did not have a symbol for "zero."
Certain rare plants containing cyanide include apricot pits and a type of potato called cassava. Fortunately, only chronic or massive ingestion of any of these plants can lead to serious poisoning.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
Urine turns bright yellow if larger than normal amounts of certain substances are consumed; one of these substances is asparagus.