Context also tells us that eating of blood is forbidden by God and that since Jesus came to fulfill the Law and not break or abolish it, then the restriction on eating blood was still in effect during the Last Supper, therefore Jesus could not have given the disciples blood to drink, and being observant Jews, they would have refused to do so if they thought it were actual, real blood.
Paul - 1 Corinthians 11:27-29 King James Version (KJV)
27 Wherefore whosoever shall eat this bread, and drink this cup of the Lord, unworthily, shall be guilty of the body and blood of the Lord.
28 But let a man examine himself, and so let him eat of that bread, and drink of that cup.
29 For he that eateth and drinketh unworthily, eateth and drinketh damnation to himself, not discerning the Lord’s body.
Guess Paul didn’t have a clue. Who knew?