The role of Prof. Myles was offered to Peter Cushing, but he refused to accept the part because of director Lucio Fulci's reputation for making gory horror-movies.
Lucio Fulci stated on numerous occasions that this film was actually directed as a favor to the producer.
During filming, a woman rushed to a group of actors dressed as policemen to seek aid after a car accident. The actors, who didn't speak English, couldn't understand the woman's pleas for help, while she mistakenly believed they were real police officers.