The Priest genuflects, takes the Host and, turning to the People, holding it slightly raised above the paten [...] says aloud:
Behold the Lamb of God, behold him that taketh away the sins of the world. (At this point the people customarily cross themselves.) Blessed are those who are called to the Supper of the Lamb.
The People respond together with Priest [said once or three times, according to custom]:
Lord, I am not worthy that thou shouldest come under my roof, but speak the word only, and my soul shall be healed.
Concomitance - the doctrine that the Body and Blood of Christ are each present in both the bread and the wine of the Eucharist.
1 Corinthians 11:27-32
Whoever, therefore, eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of profaning the body and blood of the Lord. Let a man examine himself, and so eat of the bread and drink of the cup. For any one who eats and drinks without discerning the body eats and drinks judgment upon himself. That is why many of you are weak and ill, and some have died. But if we judged ourselves truly, we should not be judged. But when we are judged by the Lord, we are chastened so that we may not be condemned along with the world.