The title Hidden refers not just to their physical location, but to their true natures hidden from themselves and the world. It challenges the audience to reconsider who the real "terror" belongs to—the infected family trying to survive, or the "healthy" society trying to exterminate them.

They carry a virus that transforms them into physically powerful, "monstrous" beings when agitated.

The central philosophical pivot of Hidden is its subversion of the antagonist. While the family fears the "Breathers" as external predators, the film eventually reveals a jarring reality: the family members themselves are the "monsters" in the eyes of society.