Drinking the blood or eating the flesh is a metaphor for found in a parable .The suffering ones own soul in jeopardy of one own spirt life.
Great parable given twice in the Old testament. It uses David imprisoned longing for the water of the gospel .God is shown sending three of the renown giants of faith to bring the water used to signify the gospel. Three representing the end of a matter.
When the men brought the living water from the Jacob's well near the city of bread Bethlehem. David poured out the work of the three calling it blood and gave glory to God. Because they went in jeopardy of their lives just as Christ did for us
2 Samuel 23:15-1 And David was then in an hold, and the garrison of the Philistines was then in Bethlehem.
And David longed, and said, Oh that one would give me drink of the water of the well of Bethlehem, which is by the gate! And the three mighty men brake through the host of the Philistines, and drew water out of the well of Bethlehem, that was by the gate, and took it, and brought it to David: nevertheless he would not drink thereof, but poured it out unto the Lord. And he said, Be it far from me, O Lord, that I should do this: is not this the blood of the men that went in jeopardy of their lives? therefore he would not drink it. These things did these three mighty men.