So let's suppose we have a well, a container, and inside that well, so on the surface of that well, we essentially place the antigens that are found in the HIV agent. So the surface of the well is coated with a specific antigen that comes from that viral agent. And these antigens are shown in red. Now, once we coat the well, we then extract the blood sample. We extract the antibodies from the blood from that individual and we take these antibodies and we place them into this well. Now, some of these antibodies will not be against the antigen and so they will not bind to that antigen.