A Catholic mass is by definition the sacrifice of Christ (Catechism 1322, 1338). The Baltimore Catechism (Confraternity Edition of 1949) says,
"Christ gives us His own body and blood in the holy Eucharist first, to be offered as a sacrifice commemorating and renewing for all time the sacrifice of the cross" (Catechism 356).
While the Catholic catechisms quote the passages that speak of Christ dying once, they also teach that the priest miraculously transforms the bread and wine into Christ's real body, and that Jesus is then sacrificed anew. "The blood is real blood (it looks like wine and tastes like wine at Mass, but it is truly the Blood of Christ." 
Although there is some variation among Protestants on the meaning of the Lord's supper, without exception biblical Protestants teach that the sacrament is not a renewal or a revisitation of the bodily sacrifice of Christ. Rather it is a remembrance and a memorial use of symbols blessed by God to the benefit of the humbled believer.
This contrast is far more than a controversy of words. It goes to the very heart of the difference between Catholicism and Protestant Christianity. Protestant faith denies that the church has the power to perform the mass's “miracle of transubstantiation,” and it further denies that the Lord's Supper's purpose is to see accomplished the death of Christ all over again.