According to Joe D'Amato, some of the heads and bones in the catacombs were plastic imitations. Upon collecting the bones after the scenes had been shot, the crew by accident took with them some real bones. Since D'Amato did not dare to return them, he let them make a "pilgrimage" to his house.
When submitted for re-classification in the UK (after being banned for 18 years), the uncut version of this film was never brought before the BBFC (British Board of Film Classification). Rather, the heavily cut, R-rated version was submitted, possibly by mistake.