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Hypertension is a silent killer because it is deadly and has no significant early symptoms. The danger from hypertension is the extra load on the heart, which can lead to hypertensive heart disease and kidney damage. This occurs without any major symptoms until the high blood pressure becomes extreme. Regular blood pressure checks are an important method of catching hypertension before it can kill you.
The familiar sounds of your heart are made by the heart's valves as they open and close.
About 3% of all pregnant women will give birth to twins, which is an increase in rate of nearly 60% since the early 1980s.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
There used to be a metric calendar, as well as metric clocks. The metric calendar, or "French Republican Calendar" divided the year into 12 months, but each month was divided into three 10-day weeks. Each day had 10 decimal hours. Each hour had 100 decimal minutes. Due to lack of popularity, the metric clocks and calendars were ended in 1795, three years after they had been first marketed.