I was asked a similar question to the one on Communion being
bloodless but on a more concrete level by a non-Christian friend who attended Mass with our family. He is very interested in Christianity and his burning question was why we say "Eat this body, drink this blood."
It really made me think more deeply how to answer someone who's vegetarian and took it quite literally. I tried to explain as best as I could but found myself inadequate as I have always believed it because Jesus said so. Maybe I should have a better understanding, especially if I am to explain it to someone else.
From the synoptic Gospels (Matthew, Mark, Luke), we learn that Jesus took bread and wine at the Last Supper and said "This is my body" and "This is my blood" and told them to eat and drink.
The Gospel of John does not have the institution of the Eucharist at the Last Supper. However, following his multiplication of loaves and fish, the words of Jesus in Chapter 6 tell us that he is the bread from heaven and that anyone who eats this bread will have eternal life. "Anyone who eats my flesh and drinks my blood has eternal life for my flesh is real food and my blood is real drink" (6:54-55). Not all of Jesus' followers could accept this and so left him.
Catholics believe that Christ is truly present, body, blood, soul and divinity in the consecrated species of bread and wine and that this change is in substance while only the appearances of bread and wine remain. The changing process traditionally has been called transubstantiation.
How are we to understand this presence? I'll let St. Thomas Aquinas the famous 13th century Catholic philosopher-theologian answer for me:
"The body of Christ is not eaten as under its natural form, but as under the sacramental species. For this reason, St. Augustine (354-430) commenting on John 6:63 (the Spirit gives life, the flesh is of no avail), said: 'This verse is directed against those who understand Christ carnally. For there are some who think that the body of Christ (in the Eucharist) is like flesh torn in strips from a corpse or sold in a butcher shop.'"
Aquinas continues: "The body of Christ in itself is not broken, but only in its sacramental appearance. And this is the sense in which we should understand Berengarius' (1059) profession of faith: 'the fraction and chewing with the teeth' refer to the sacramental species, underneath which the body of Christ is really present" (Summa IIIa.77.7, ad tertium).
It is clear, therefore, that this is what the Church has believed through the centuries and expressed through its theologians. So, we believe that Christ is present fully as man and God in the sacred species but we must not take it so carnally, as Augustine said and Aquinas confirmed. In other words, one can say that we do not bite into an arm or leg when we receive the sacred host. Nor are we all cannibals eating human flesh. Consequently, vegetarians can rest assured that they can receive Communion without any qualms.