When a runner pushes the body past the usual workout routine tolerance, it is normal to experience a blood taste in the back of the throat. The bloody taste is caused by red blood cells popping. When red blood cells are strained, they release an iron-containing compound called heme which results in the metallic taste in the mouth. It is also possible for red blood cells to leak into air sacs during extreme conditions. The unpleasant taste should be temporary, but it is important to notice if the sensation happens all the time. The recurrence of a bloody taste could be a sign of a health issue, and one should see a doctor to avoid serious problems.