With all due respect, any attempt to determine what the "jews knew" is purely conjecture. All we have is the Scriptural evidence that something He said was a big enough problem to them to cause them to reject Jesus; ("...many of his disciples turned back and no longer went about with him. - John 6:66) Perhaps you proof actually proves the opposite.
Peace be with you
With the same due respect, go back and reread the comment that mine was addressing. That is why I began mine with "the Jews...". But, yes, let's look at that passage in John 6 and see when and what Jesus had specifically said that caused many of his disciples to turn back. Beginning at John 6:53ff:
53 Jesus said to them, “Very truly I tell you, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you. 54 Whoever eats my flesh and drinks my blood has eternal life, and I will raise them up at the last day. 55 For my flesh is real food and my blood is real drink. 56 Whoever eats my flesh and drinks my blood remains in me, and I in them. 57 Just as the living Father sent me and I live because of the Father, so the one who feeds on me will live because of me. 58 This is the bread that came down from heaven. Your ancestors ate manna and died, but whoever feeds on this bread will live forever.” 59 He said this while teaching in the synagogue in Capernaum. 60 On hearing it, many of his disciples said, “This is a hard teaching. Who can accept it?” 61 Aware that his disciples were grumbling about this, Jesus said to them, “Does this offend you? 62 Then what if you see the Son of Man ascend to where he was before! 63 The Spirit gives life; the flesh counts for nothing. The words I have spoken to you—they are full of the Spirit and life. 64 Yet there are some of you who do not believe.” For Jesus had known from the beginning which of them did not believe and who would betray him. 65 He went on to say, “This is why I told you that no one can come to me unless the Father has enabled them.” 66 From this time many of his disciples turned back and no longer followed him. 67 “You do not want to leave too, do you?” Jesus asked the Twelve. 68 Simon Peter answered him, “Lord, to whom shall we go? You have the words of eternal life. 69 We have come to believe and to know that you are the Holy One of God.” 70 Then Jesus replied, “Have I not chosen you, the Twelve? Yet one of you is a devil!” 71 (He meant Judas, the son of Simon Iscariot, who, though one of the Twelve, was later to betray him.)
So, it appears that the disciples found Jesus' words a "hard saying" -as any observant Jew WOULD have considering the ban on the drinking of blood - but they actually stuck around a bit more, didn't they? Jesus proceeds to tell them more. That, I propose is why they left following him. Many problems with interpretation can be avoided if we follow through on the thought being presented rather than stopping at a point and conjecturing. It should be patently obvious that Jesus did NOT rip off a piece of his flesh and have them pass it around nor did he drain a cup of his precious blood to be sipped at by those who stayed, but he said quite clearly that HE was the real, true Bread of Life and it HAD to be a spiritual connotation. It is the SPIRIT that gives life, the flesh profits nothing. The blood that our Savior shed on the cross for our sins is the complete propitiation for sin. It is FOREVER perfecting those who are made holy through it - and it is received by faith, belief. That's what Peter said to Him, "We have come to believe and to know that you are the Holy One of God." not, "Hey, rip off some of that flesh so we can be saved!" I get the idea that Peter knew what Jesus meant.
The very elements that Catholics consume in the Eucharist are NOT literally changed - no matter how much protest and insistence is made that they are. They REMAIN and retain the same properties that they started out as and the only change is the spiritual perception of the ones partaking. If there is no "miracle" of these elements being visibly changed every time they are "consecrated", then why is a Catholic Eucharistic celebration any more holy or efficacious than that of another Christian group that observes the remembrance celebration? That is really the point. A Catholic who "receives" the communion wafer is no more sanctified than someone else who has believed on the Lord Jesus Christ as Savior and participates in his own church's communion service, remembering the body and blood of Christ given for his salvation. I think there is a real problem with some Catholics who use this issue to convert and convince those who don't know what Scripture says and to make it an issue of "believe US or call Jesus a liar", really goes TOO far. Those who persist in provoking this argument are not doing it for the cause of love or unity in Christ.
I sincerely wish you peace, as well.