Why do you think the Jews in John 6 were so shocked, disgusted, offended with what Jesus said? Would they have been so flabbergasted if they thought He was making a point with a colorful simile? (Wooh, what a wordsmith.) Come on! They were outraged with Him replacing the dietary law with a banquet of His Body and Blood.
There's a lot about the abolition of the kosher laws in Acts, and about the realism of Jesus' Body and Blood which we are to eat and drink, in 1 Corinthians.
This is why Acts and the Epistles are essential to our understanding of New Testament worship.
If Rome wants to continue to try and compare the sacrifice of Christ with the OT sacrifice, they will have to admit, though they don't, that blood was shed for the forgiveness of sin.
When Christ shed His blood on the Cross that was the sacrifice for our sin.
If the disciples believed as Rome claims that we are to eat/drink His flesh and blood they would have been at the Cross capturing His blood.
If they believed this Thomas had an opportunity to "drink" His blood when he put his fingers into His side.
There were more than ample opportunities for the disciples to have eaten/drunk His flesh and blood.
We have ZERO accounts of this ever happening. Rome's understanding of the texts are incorrect on this, and many other, matters.
The liquid in the cup is the fruit of the vine. As others have attested, it does not change into His blood as the person drinking the cup does not detect a change.
The Holy Spirit reiterated the prohibition against eating blood.
The prohibition against eating blood started BEFORE the Law and was reiterated after Jesus fulfilled it.
It stands outside the Law, unlike other aspects of the Law that no longer are required.
Acts 15:12-29 And all the assembly fell silent, and they listened to Barnabas and Paul as they related what signs and wonders God had done through them among the Gentiles. After they finished speaking, James replied, “Brothers, listen to me. Simeon has related how God first visited the Gentiles, to take from them a people for his name. And with this the words of the prophets agree, just as it is written,
“‘After this I will return, and I will rebuild the tent of David that has fallen; I will rebuild its ruins, and I will restore it, that the remnant of mankind may seek the Lord, and all the Gentiles who are called by my name, says the Lord, who makes these things known from of old.’
Therefore my judgment is that we should not trouble those of the Gentiles who turn to God, but should write to them to abstain from the things polluted by idols, and from sexual immorality, and from what has been strangled, and from blood. For from ancient generations Moses has had in every city those who proclaim him, for he is read every Sabbath in the synagogues.”
Then it seemed good to the apostles and the elders, with the whole church, to choose men from among them and send them to Antioch with Paul and Barnabas. They sent Judas called Barsabbas, and Silas, leading men among the brothers, with the following letter:
“The brothers, both the apostles and the elders, to the brothers who are of the Gentiles in Antioch and Syria and Cilicia, greetings. Since we have heard that some persons have gone out from us and troubled you with words, unsettling your minds, although we gave them no instructions, it has seemed good to us, having come to one accord, to choose men and send them to you with our beloved Barnabas and Paul, men who have risked their lives for the name of our Lord Jesus Christ. We have therefore sent Judas and Silas, who themselves will tell you the same things by word of mouth. For it has seemed good to the Holy Spirit and to us to lay on you no greater burden than these requirements: that you abstain from what has been sacrificed to idols, and from blood, and from what has been strangled, and from sexual immorality. If you keep yourselves from these, you will do well. Farewell.”