According to the Catholic doctrine of Transubstantiaion the bread and the wine actually transform into the actual material blood and body of Christ. Personally I do not believe this and I think there are a number of great arguments against it. However, in this blog I will detail only one of them.
This isn't the only time people have confused Christ's words for something material when they were supposed to be spiritual. Jon Courson writes:
In John 3, Jesus said, "You must be born again."
"How does a man enter into his mother's womb the second time?" asked Nicodemus. Jesus was speaking spiritually, but Nicodemus was trying to figure it out physically.
In John 4, Jesus said, "I have water to give you which if you drink you shall never thirst again."
"Give me this water," said the woman at the well, "so I won't have to keep drawing water from the well." She was thinking materially, but Jesus was speaking about the water of the Spirit internally.
In John 6, Jesus said, "Unless you eat of My body and drink of My blood, you can have no part of Me."
The crowds, thinking He was talking about cannabalism, began to turn away from Him. Again, He was speaking of the spiritual realm, but the people couldn't see past the material realm.
This seems to be our nature to generally not comprehend what Jesus is talking about unless the Holy Spirit tells us.