When Saunière arranged his own dying body into a bizarre tableau of symbolism, one of the features that Fache felt he should focus on understanding was the fact that he'd inscribed a pentagram onto his stomach using his own blood.
Pentagram. Onto his stomach. Using his own blood.
That is so metal.
When he asks Langdon for his interpretation of Saunière choice of imagery the professor explains:
"The pentacle," Langdon clarified, "is a pre-Christian symbol that relates to Nature worship. The ancients envisioned their world in two halves— masculine and feminine. Their gods and goddesses worked to keep a balance of power. Yin and yang. When male and female were balanced, there was harmony in the world. When they were unbalanced, there was chaos."
Langdon motioned to Saunière's stomach. "This pentacle is representative of the female half of all things— a concept religious historians call the "sacred feminine" or the "divine goddess."
Saunière, of all people, would know this."
"Saunière drew a goddess symbol on his stomach?"
Langdon had to admit, it seemed odd.
"In its most specific interpretation, the pentacle symbolizes Venus— the goddess of female sexual love and beauty."
Fache eyed the naked man, and grunted. (6.41-44)
Fache was thinking the more obvious (and obviously metal) thing—that the pentacle referred to devil worship or witchcraft of some kind—but Langdon helpfully points out that that's a fallacy created by the Catholic Church's smear campaign against worshipping the sacred feminine, which has been irresponsibly promoted by Hollywood:
"I assure you," Langdon said, "despite what you see in the movies, the pentacle's demonic interpretation is historically inaccurate. The original feminine meaning is correct, but the symbolism of the pentacle has been distorted over the millennia. In this case, through bloodshed." […]
"Symbols are very resilient, but the pentacle was altered by the early Roman Catholic Church. As part of the Vatican's campaign to eradicate pagan religions and convert the masses to Christianity, the Church launched a smear campaign against the pagan gods and goddesses, recasting their divine symbols as evil." (6.50-52)
So basically, according to Langdon, we have Hollywood and the Catholic Church to credit turning the pentagram from a symbol of the sacred feminine to a symbol of…the devil. Huh. Come to think of it, that's also pretty freaking metal.