Luigi Montefiori, aka George Eastman, who wrote, and portrayed the disfigured cannibalistic serial killer Klaus Wortmann stated that when he went to the premier at the old Cinema Metropolitan in Rome with the producer, only a few people were in the theater watching. During the film people kept walking out until only a single couple remained. Later, during the scene where the pregnant woman was strangled and had her foetus ripped out of her, the couple got up and walked out offended. (In real life the effect was achieved using a skinned rabbit, and was something new and very disturbing for the time.) Montefiori and the producer ended up the only ones left watching the rest of the film.
According to Joe D'Amato, some of the heads and bones in the catacombs were plastic imitations. Upon collecting them after the scenes had been shot, the crew accidentally took with them some real bones. Since D'Amato did not dare to return them, he let them make a "pilgrimage" to his house.