And that's exactly what the function of hemoglobin is. So myoglobin is used to actually store that oxygen in the muscle cells, while hemoglobin is used to actually carry the oxygen from the lungs through the bloodstream into the tissues and cells of our body. And only when the hemoglobin isn't able to actually bring enough oxygen to our cells, only then does myoglobin begin to release that oxygen to the muscle cells of our body. So the sigmoidal curve is produced as a result of hemoglobin's ability to bind oxygen in a cooperative fashion. So earlier we said that myoglobin binds oxygen in a non cooperative fashion, while hemoglobin binds it cooperatively. So what do we mean by that?