Why do you suppose that the influenza virus protein that binds the virus to an infected cell is called hemagglutinin? hemagglutination is the clumping together of red blood cells?

Agglutination, is the state of being united, i. e the adhesion of parts. Thus, hemagglutination is adhesion of red blood cells. The protein that binds the virus to an infected red blood cell is thus called hemagglutinin, because, it binds to multiple red blood cells, causing them to clump together.