They didn't. Read verses 59 - 61 when the disciples leave. No mention of them mumbling about flesh. Then verse 67, Jesus says," Will ye also go away??" To which Peter replies in verse 68 and 69, ".."Lord, to whom shall we go? Thou hast the words of eternal life. [69] And we believe and are sure that thou art that Chirst, the Son of the living God.
Look back now at verse 64..."For Jesus knew from the beginning who they were that believed not, and who should betray him."
It wasn't about eating flesh that the disciples split and ran over. The rest of the passage betrays that clearly. The problem was unbelief. And Peter sums it up and says, 'hey, who would we follow. The rest of us believe in you.' Of Course, Jesus turns around and says, 'Yeah, all but one - who is a devil'.
Now to drive the stake further in, look at verse 62. "What and if ye shall see the Son of man ascend up where he was before?" Or in other words, 'What will it take for you to believe in me at this point, seeing me asend to heaven?' He's arguing His case, not about eating flesh - that was but a metaphor applied to the original statements about belief in Him. It's all there plain as the nose on your face. It loses it's planeness when you start trying to shove it in your doctrine box and refuse to see more than you are told. That is your problem. The scripture speaks quite well for itself there.
"Jesus said to them, 'I am the bread of life; he who comes to Me shall not hunger, and he who believes in Me shall never thirst.'"
Compare that verse with verse 54:
"He who eats My flesh and drinks my blood has eternal life."
In other words:
"eats My flesh" = "comes to Me" (result: shall not hunger, i.e., "have eternal life")
"drinks My blood" = "believes in Me" (result: shall not thirst, i.e., "have eternal life")
Talk about the Great Communicator; that was Jesus!!
Anyway, thanks again.