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When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
When blood is deoxygenated and flowing back to the heart through the veins, it is dark reddish-blue in color. Blood in the arteries that is oxygenated and flowing out to the body is bright red. Whereas arterial blood comes out in spurts, venous blood flows.
The familiar sounds of your heart are made by the heart's valves as they open and close.
Pope Sylvester II tried to introduce Arabic numbers into Europe between the years 999 and 1003, but their use did not catch on for a few more centuries, and Roman numerals continued to be the primary number system.
Drying your hands with a paper towel will reduce the bacterial count on your hands by 45–60%.