Theodore of Mopsuestia on John 6

 "After our Lord had said these things, clearly indicating that the word bread referred to his body because it was to be eaten, the Jews argued again with each other, saying, [6:52] How can this man give us his flesh to eat? When nature itself does not allow this. And they opposed what he was saying as something difficult and sinful as though he were asking them to really eat human flesh." (Theodore of Mopsuestia, Commentary on the Gospel of John, on 6:52, source)