Argento didn't want to use the "image caught in the retina" plot device since it was too fantastic for the giallo genre. But once Carlo Rimbaldi showed him how the effect would look like in the finished film, he soon changed his mind.
This was originally intended to be Argento's swan song to the giallo genre. This would later change once Five Days of Milan did poorly at the box-office.
Argento's usual collaborator Ennio Morricone scored the film but had a major argument with Argento over some tracks Argento didn't want in the film. As a result, the director and Morricone would never work together again until 1996, and the rock group Goblin would eventually become Argento's regular composers.