So we have this blood capillary and we have the deviation in the blood capillary as shown. Now, these are the normal healthy biconcave red blood cells and because of their bi concave nature they will easily and effectively be able to squeeze through the tiny capillaries of our cardiovascular system and they will not bind, they will not aggregate to one another. Now, when the red blood cells transform their biconcave shape into the sickle shape, these sickle shaped red blood cells will begin to aggregate and that can lead to clogging of these capillaries. So for example, if we clog this region of the capillary, what that does is it increases the pressure on this side and that can push against the walls of the capillaries and that can lead to very painful swelling. On top of that, if we clogged this section then there will be poor blood flow in this region of our capillary and that can lead to poor circulation of the blood in the cardiovascular system. And this in turn can lead to an increased risk of stroke because stroke, remember, is the process by which we don't get enough blood and don't get enough oxygen to the brain.