Those two human "sculptures" have lived beneath the chapel for over 200 years, meaning that they've been creeping people out since way before posing fleshless bodies went mainstream. The male-and-female pair, dubbed Adam and Eve, used to also include a freaking fetus, but it was either stolen or it escaped on its own and is standing behind you right now. These are the only two possibilities.
Yet somehow, stolen, decorated fetus skeletons aren't even the freakiest part of this holy site. That honor goes to the so-called "black legend" of Raimondo di Sangro, the Prince of Sansevero, otherwise known as the guy responsible for these "Anatomical Machines." As well as being an alchemist, inventor, Naples' highest-ranked Masonic leader and probably a super fun person to hang with at parties, the prince was also the repository of many, many disturbing stories. Villagers suspected that he dabbled in the dark arts, and had discovered a process of injecting blood vessels to turn them into metal -- the implication being that the models for Adam and Eve were two house servants that he murdered and turned into large biology class props.
Sansevero Chapel Museum
The servant who had the eyes plucked out was the lucky one.