The Mass. There is no mistaking it. Fundamentalists do not like the Mass, and they like it even less that they otherwise might because they misunderstand what it is.
The RCC teaches that the Holy Mass is an expiatory (sin-removing) sacrifice, in which the Son of God is actually sacrificed anew on the cross. Keating (an RC apologist)
Vatican II, puts it this way:
At the last supper, on the night he was betrayed, our Savior instituted the Eucharistic Sacrifices of his body and blood.
He did this in order to perpetuate the sacrifice of the cross throughout the centuries until he should come again, and so to entrust to his beloved spouse, the Church, a memorial of his death and resurrection: a sacrament of love, a sign of unity, a bond of charity, a paschal banquet in which Christ is consumed, the mind is filled with grace, and a pledge of future glory is given.
@Arch Stanton to be fair I added the RC apologist and Vatican II