The Eucharist can actually be seen as sacrificing to idols.
(Revelation of John 2:14 [KJV]) But I have a few things against thee, because thou hast there them that hold the doctrine of Balaam, who taught Balac to cast a stumblingblock before the children of Israel, to eat things sacrificed unto idols, and to commit fornication.
This is because of that the priest claims to turn the bread into the body of Christ. Then the bread is eaten. So its a sacrifice again of Jesus Christ. Also its an idol because this bread is not the lord Jesus Christ but they claim it is. They also i think bow down to it. So they worship an idol.
(Leviticus 26:1 [KJV]) Ye shall make you no idols nor graven image, neither rear you up a standing image, neither shall ye set up any image of stone in your land, to bow down unto it: for I am the LORD your God.
Also the priest claims to turn the wine into the blood of Jesus Christ. But we are told not to eat blood.
(Deuteronomy 12:23 [KJV]) Only be sure that thou eat not the blood: for the blood is the life; and thou mayest not eat the life with the flesh.
Anyone who claims that the communion is anything more than in remembrance of Jesus Christ, is involved in this error.
(I Corinthians 11:24-25 [KJV])  And when he had given thanks, he brake it, and said, Take, eat: this is my body, which is broken for you: this do in remembrance of me.  After the same manner also he took the cup, when he had supped, saying, This cup is the new testament in my blood: this do ye, as oft as ye drink it, in remembrance of me.