Besides a literal understanding of this being required if Catholics are going to be consistent with a professed literal understanding of John 6, yet such being clearly untenable in the light of the rest of the NT that follows, such language is consistent with John's use of metaphorical language, using the physical to refer to the spiritual:
• In John 1:29, Jesus is called “the Lamb of God, which taketh away the sin of the world” — but he does not have hoofs and literal physical wool.
• In John 2:19 Jesus is the temple of God: “Destroy this temple, and in three days I will raise it up” — but He is not made of literal stone.
• In John 3:14,15, Jesus is the likened to the serpent in the wilderness (Num. 21) who must “be lifted up: That whosoever believeth in him should not perish, but have eternal” (vs. 14, 15) — but He is not made of literal bronze.
• In John 4:14, Jesus provides living water, that “whosoever drinketh of the water that I shall give him shall never thirst; but the water that I shall give him shall be in him a well of water springing up into everlasting life,” — but which was not literally consumed by mouth.
• In John 7:37 Jesus is the One who promises “He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water” — but believers were not water fountains, but He spoke ”of the Spirit, which they that believe on him should receive.” (John 7:38)
• In Jn. 9:5 Jesus is “the Light of the world” — but who is not blocked by an umbrella.
•I n John 10, Jesus is “the door of the sheep,” and “the good shepherd [who] giveth his life for the sheep”, “that they might have life, and that they might have it more abundantly” vs. 7, 10, 11) — but who again, is not literally an animal with cloven hoofs.
• In John 15, Jesus is the true vine — but who does not physically grow from the ground nor whose fruit is literally physically consumed.
And which is consistent with the abundant use of figurative language which preceded it, such as where the Canaanites were said to be "bread" for Israel, and David called potable water the "blood" of men, and thus refused to drink it, and poured it out unto the Lord. (2 Samuel 23:16-17)
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. (2 Samuel 23:16-17)
Here, David clearly calls drinking water human blood, and consistent with the command of Deuteronomy 12:16; 15:23 (cf. Lv. 17:10,11), he poured it on to the ground, and did so as an act of worship unto the Lord. What David did not do was contrive some metaphysical justification for drinking this, but to be consistent with the professed plain-language hermeneutic Catholics insist they hold to in regards to "this is my body," then they should also insist this was literal in this case. As well as when God clearly states that the Canaanites were “bread:
• “Only rebel not ye against the LORD, neither fear ye the people of the land; for they are bread for us” (Num. 14:9)
Other examples of the use of figurative language for eating and drinking include,
• The Promised Land was “a land that eateth up the inhabitants thereof.” (Num. 13:32)
• David said that his enemies came to “eat up my flesh.” (Ps. 27:2)
• And complained that workers of iniquity ”eat up my people as they eat bread , and call not upon the Lord.” (Psalms 14:4)
• And the Lord also said, “I will consume man and beast; I will consume the fowls of the heaven, and the fishes of the sea, and the stumblingblocks with the wicked; and I will cut off man from off the land, saith the Lord.” (Zephaniah 1:3)
• While even arrows can drink: “I will make mine arrows drunk with blood, and my sword shall devour flesh ; and that with the blood of the slain and of the captives, from the beginning of revenges upon the enemy.' (Deuteronomy 32:42)
• But David says the word of God (the Law) was “sweeter also than honey and the honeycomb. (Psalms 19:10)
• Another psalmist also declared the word as “sweet:” “How sweet are thy words unto my taste! yea, sweeter than honey to my mouth!” (Psalms 119:103)
• Jeremiah likewise proclaimed, “Your words were found. and I ate them. and your word was to me the joy and rejoicing of my heart” (Jer. 15:16)
• Ezekiel was told to eat the words, “open thy mouth, and eat that I give thee...” “eat that thou findest; eat this scroll, and go, speak to the house of Israel.” (Ezek. 2:8; 3:1)
• John is also commanded, “Take the scroll ... Take it and eat it.” (Rev. 10:8-9 )
And Scripture refers to Christ being spiritual food and drink which even OT believers consumed:
• And did all eat the same spiritual meat; "And did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ." (1 Corinthians 10:3-4)
• And Christ's word in Jn. 6, "I am the bread of life: he that cometh to me shall never hunger; and he that believeth on me shall never thirst," (John 6:35) are correspondent to,
"Wherefore do ye spend money for that which is not bread? and your labour for that which satisfieth not? hearken diligently unto me, and eat ye that which is good, and let your soul delight itself in fatness. Incline your ear, and come unto me: hear, and your soul shall live; and I will make an everlasting covenant with you, even the sure mercies of David." (Isaiah 55:2-3)
• Moreover, like as bread is broken, Is. 53:10 states that "it pleased the Lord to bruise him," and the word for "bruise" (da^ka^') means to crumble, to break..., (Strong's). And like as wine is poured out, so Is. 53:12 also states of Christ, "he hath poured out his soul unto death," both of which are correspondent to the words of the Last Supper regarding bread and wine.