Can't say anything more than this: Such a passage is meant to be stumbling block for unbelievers. For Christ later "contradicts" himself by saying "the spirit gives life, the flesh is of no avail." He is not really contradicting himself but rather explaining that he gave a "hard saying to the Jews and his disciples to see if anyone is able to see the "spiritual" reality behind the words ("metaphorical", if you'd like but metaphorical is such a wussy word for us moderns and does not convey the importance that symbolism and metaphor had for ancient world).
The Spirit of the Resurrection gives life to even to this difficult, seemingly "fleshly," even cannibalistic passage. (Christians in the early Church were actually accused of cannibalism)
Why doesn't Christ tell them "I was being metaphorical." For the same reason that he only speaks to the people in parables in Mark's Gospel, to paraphrase: "If I spoke to them clearly, then they would turn from their wicked ways and live."
Christ's hard sayings, (i.e. parables, allegories, metaphors) simply reinforce the fact that hard hearts produces hard minds.
Frank Kermode's book, "The Genesis of Secrecy" discusses Christ's parables from the point of view of an unbeliever. He comes to the conclusion that they are impenetrable. Yet so is the cross for those searching for signs or wisdom.



P.S. I forgot to let everyone know that I was ordained to the diaconate. Sorry. Please pray for me in my new ministry.

Jesus didn't go out & gather a crowd to proclaim this hard teaching--it was a response to a crowd (the one he miraculously fed) coming to him.
So going into the conversation, the crowd already saw him do a miracle and called him The Prophet promised by Moses.
They searched all over Galilee for him (he lost them by walking across the lake), and when they found him, he responded to their arrival by saying, "You guys didn't looking for me because of the miraculous sign--I just fed you well."
So first off, he points out that they aren't looking for him because he's The Prophet, but because he did something for them.
The ensuing conversation about them needing to eat Jesus' flesh is a confronataion to them, showing them they aren't really pursuing The Prophet himself, but the relief he brings to their current situation.
(I imagine they expected The Prophet "with further instructions" to be another Moses to free them from slavery again...and maybe get them a little further along the path to being the nation that blesses all nations)

I don't get it that this is a parable... If it is it sure is different from any I recall... There is no story or explanation time afterwards for the disciples, Peter does his statement of faith right after... With parables the disciples are always like "WHHHHAAAT???"