What about them? Who are they? How does one recognize them in the long line of communicants? What if the individual went to confession prior to the mass? How is that information communicated to the priest or EMHC distributing communion?
Only God can read the hearts of man. You will find your answer in Scripture. In 1 Corinthian 11:27, Paul says that eating or drinking in an unworthy manner is equivalent to profaning (literally, murdering) the Body and Blood of the Lord. In the same Chapter of 1 Corinthians, Paul continues by saying, ""For all who eat and drink without discerning the body, eat and drink judgment against tehmselves. For this reason many of you are weak and ill, and some have died." [1 Cor. 11:29-30] In other words, those who receive the Sacrament of the Holy Eucharist in an unworthy manner, in a state of mortal sin, they can expect to be punished by God by illness or death.
If they are public sinners like pro-abort politicians they must make their change of heart public.
They're usually the people who have obama bumper stickers on their cars in the parish parking lot. Either that or they're a member of the US Congress.
If they look like Nancy Polosi or Ted Kennedy, vocal advocates of "a woman's right to choose", absent an equally vocal retraction of said advocacy, they're baby-killers.