From Fr. Andrew Trapp’s conversation with a former Satanist in France:
The poor guy probably felt like he was being interrogated by the CIA by this point, but knowing that I might never have this opportunity again, I asked Nicolas one final question. I told him that I had also heard that those who were very deep in Satanism could actually tell whether a communion host had been consecrated or not. For example, they will not steal communion bread from Protestant communion meals, nor will they steal unblessed communion bread for desecration at these “Black Masses.” It would not work because some of the Satanists would immediately recognize that it was just ordinary bread. They would be able to tell that Jesus Christ was not sacramentally present there.
I asked Nicolas whether this also was true. He again replied that it is, and he told us that he could do this himself before his conversion from Satanism. A chill went down my spine. If someone were to put ten identical communion hosts in front of him, nine unconsecrated and one consecrated, he would have been able to point directly and immediately to the host that had been consecrated. I asked him in amazement, “But how were you able to know?!?” He looked at me and the words he spoke are forever burned in my memory: “Because of the hate,” he said. “Because of the burning hate I would feel toward that host, apart from all the others.”
[B]e reminded that Satan’s favorite trick–his favorite lie is to tell you that he does not exist. This lie comes in several forms. The most blatant is to tell you that he and God both do not exist. The second form is to let you believe in God, but to tell you that he doesn’t exist; that such a belief is medieval or superstitious. That is his lie. Do not believe it. The third form of the lie is that he is not a real personal entity, that “the Devil” is simply another name for evil or “the shadow” or “the dark side of the force.”