It causes a change in the three dimensional structure of the entire hemoglobin. And as the structure changes, it makes it much more likely to actually pick up other oxygen molecules. So as soon as our deoxy hemoglobin picks up a single oxygen, it changes its shape ever so slightly, and it changes the shape in such a way that it makes it much more likely to pick up other oxygen molecules. Likewise, when our hemoglobin is fully saturated with oxygen and one of those oxygen molecules actually dissociates, that dissociation process creates a conformational change in the hemoglobin that causes it to be more likely to dissociate the other three oxygen molecules. And this process, this type of behavior of hemoglobin, is referred to as positive. Cooperativity so the question is, what will make our hemoglobin actually release an oxygen?