Blood is a bodily fluid, potentially one of the most important of all specialised fluids. The importance of blood is that it travels throughout the body delivering necessary substances to the bodies cells and organs, for instance nutrients and oxygen. As well as this, blood transports all the bodies waste away from the cells and organs ready for said waste to be expelled from the body. Without blood, the body would fail to get the substances it needs, nor would it manage to excrete the waste that could potentially do some damage. The pumping action of the heart pushes blood through blood vessels throughout the body in order to allow the blood to do it's job. If these blood vessels are severed, blood will spill out and can have serious effects ranging from treatable to irrepairable. If the skin is broken and a near by blood vessel is severed, blood will spill out of the body where it appears to be red in colour and tastes of metallic. This is because red blood cells carry Hemoglobin, an iron-containing protein.
Blood has played a prominent part in video games throughout the ages, most likely because its bright red colour is easily distinguishable and can easily indicate the sort of damage that has been dealt to an enemy. As well as that, blood is an effective way of showing that any damage at all has been dealt as an obvious first instinct when one sees blood is that someone has been injured.