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.
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.
What are the differences between the US VHS Version (Silver Star) and the UK VHS Version (Virtual Assassin)?
A
Both versions are incomplete. The UK VHS offers four longer sequences that are not featured on the American VHS whereas the US VHS does include two short scenes that are missing in the UK VHS. A detailed comparison between both versions can be found here (UK <-> US) and here (US <-> UK)