Blood

Blood is a liquid contained by the circulatory system of many vertebrates, including humans, nerpas, and all other varieties of seal. Blood is famously red, the color of love, although it is true that blood can sometimes be blue or even green.

Blood is made of blood cells suspended in blood plasma which sounds totally awesome and cool but its actually not. It's quite boring. Blood is required in large quantities for all organisms that have it (aside from the Aral seal, which has a body that contains only a single drop of the substance).

Blood is so important because it carries oxygen from the respiratory system to the body's many cells, which require the oxygen to stay alive, function, and reproduce! Blood also removes the waste carbon dioxide from the cells, which is brought back to the lungs to be exhaled. Many other important chemicals are also circulated with blood, including hormones, important proteins such as amino acids and lipids, coagulants to prevent major loss of blood, and poisons that kill you.

You can also kill people by draining all of their blood from their body, this technique was proven to work through The Killer's ingenious and groundbreaking scientific discoveries.