In catholiciism, drinking of blood is an accepted and indeed commanded ritual, which is anathema to the foundations of Christianity which is the direct child of the pact GOD gave to Abrahama and his descendants, and which was made more stringent by the giving of the laws which Jesus said would never pass away. In catholiciism, the laws they believe have passed away because they presume to drink the blood of GOD at their Mass rituals. That is quite the pagan rite, but that should not surprise anyone who knows how the father of lies works among men.
We could cite aspects of catholiciism's Mariology and show how these also are not an aspect of Christianity. We could enumerate the practice of praying to dead people given the title of Saints by the magisterium, who may not even be Christians! But we know these things and it is more and more apparent that catholiciism is not Christiantiy, so if these sincere people want to believe this 'other religion', this 'other gospel', where one must eat GOD and Drink GOD's blood to get God-life in them, let us not try to argue them that these things do not belong in Christianity, they are aspects of another gospel that is not Christianity anyway!
Their Catholicism is completely UNLIKE Christianity where Jesus told us that believing in Him we have eternal life, then, and He will place Holy Spirit in us then, not after striving for the rest of a life to be worthy of deliverance. God even left for us record of how it works as the scene in Acts on the Day of Pentecost illustrated, and the coming of the Holy Spirit in the house of the Roman Centurion, Cornelius. This system of catholiciism is so clearly anathema to all the Bible instructs that we should understand these people are practicing an 'other gospel'.
John MacArthur has said that catholics are a very ripe evangelism field, but we must be ready to show the dichotomy and use The Bible to back up our assertions. These catholic apologists refuse to hear the Truth, but an average catholic may be no more knowledgeable than a typical Mormon. Behold, the hour is late and the fields are ripe for missions.
Meant to ping you, Bro.