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This year, an estimated 1.4 million Americans will have a new or recurrent heart attack.
Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
Vaccines prevent between 2.5 and 4 million deaths every year.
The heart is located in the center of the chest, with part of it tipped slightly so that it taps against the left side of the chest.
The human body produces and destroys 15 million blood cells every second.
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