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Every 10 seconds, a person in the United States goes to the emergency room complaining of head pain. About 1.2 million visits are for acute migraine attacks.
The familiar sounds of your heart are made by the heart's valves as they open and close.
Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
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.
Giardia is one of the most common intestinal parasites worldwide, and infects up to 20% of the world population, mostly in poorer countries with inadequate sanitation. Infections are most common in children, though chronic Giardia is more common in adults.