The idea of the pins-under-the-eyes torture device came from a joke of Argento's. Argento said it would annoy him when people would look away during the scary scenes in his films. He would jokingly suggest taping pins under people's eyes so they couldn't look away from the film. It would late materialize on the screen for this film.
According to star Urbano Barberini, it would take hours for everyone to re-capture the crows after they were released in the opera house for filming. Around 140 crows were used, but only 60 sum were ever retrieved. The others apparently escaped from the opera house during filming.
In the book "Profondo Argento", Dario Argento cited star Cristina Marsillach as the most difficult actress he has ever worked with.
Orion, the American distributor of the film, wanted Argento to cut the final scenes in the Swiss countryside out of the film. Argento refused.
Many mishaps on set, including the death of one of the actors, led director Dario Argento to believe that the "Macbeth curse" also struck during the making of this film.