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Each year in the United States, there are approximately six million pregnancies. This means that at any one time, about 4% of women in the United States are pregnant.
The familiar sounds of your heart are made by the heart's valves as they open and close.
On average, someone in the United States has a stroke about every 40 seconds. This is about 795,000 people per year.
After a vasectomy, it takes about 12 ejaculations to clear out sperm that were already beyond the blocked area.
Hippocrates noted that blood separates into four differently colored liquids when removed from the body and examined: a pure red liquid mixed with white liquid material with a yellow-colored froth at the top and a black substance that settles underneath; he named these the four humors (for blood, phlegm, yellow bile, and black bile).