Now, as they use up oxygen, that decreases the concentration of oxygen in the cells of the tissue, and that therefore decreases the partial pressure of oxygen in our tissue. And that's exactly why we have this difference in pressure now, because oxygen will always move naturally from a higher partial pressure to a lower partial pressure. As our red blood cells move along our capillary, our hemoglobin will unload our oxygen. The oxygen will dissociate. And as one oxygen dissociates, it makes the other oxygens more likely to dissociate. And this is positive.