The best way a person can make a clear literal point is
repetition of the same message in different ways. Jesus did
this. Those around him clearly understood what he was
saying--cannibalism and the drinking of blood--both forbidden
by Mosaic Law.
Then many of his disciples who were listening said,
"This saying is hard; who can accept it?" ... As a result
of this, many (of) his disciples returned to their former
way of life and no longer accompanied him.
Had these disciples mistaken the meaning of Jesus' words,
Jesus, knowing their thoughts and their error, would surely
have known and corrected them. He didn't. They had clearly
understood his meaning--Jesus' flesh was to be really eaten;
his blood to be really drunk.