The Eucharist is a symbolic meal when Christians eat the body of Jesus symbolized by bread and drink the blood of Jesus symbolised by wine. Didn't you always think cannibalism is wrong? Different Christian Denominations have different beliefs about exactly what happens during the Eucharist and in the past were prepared to kill and die for their particular version of the Mythology.
Protestant Christians do not always believe the bread and wine are literally the body and blood of Jesus, and prefer to all their own version of this "The Lord's Supper" or "Holy Communion" and it all gets very complicated.
Flying Spaghetti Monster