what is your central idea of the use of blood in macbeth? Generally, blood is used to reinforce the fear of killing/be killed.

Can you do an analogy to Blood on Blood? Both deal with killers and while Macbeth uses blood as a threating device, the song uses blood as a bond - kind of a comfort of not getting killed by your "blood-brother".

Not sure if you could really develop an analogy, though. Just a thought.