Argento's "animal trilogy", beyond the fact that titles all bear a reference to an animal (bird, cat, flies), has an essential common point: a founding scene which is the pivotal element of the film, giving birth to a twisted mystery, and which is in one way or the other staged. Literally in isolation from the rest of the film.
In "The Bird with the crystal plumage", this scene is obviously the art gallery crime sequence, which is precisely defined and isolated by the frame of the massive glass window from the street and the city life.
A different illustration of the same principle is found in "The cat o'nine tails", where the founding scene is not visual, but audio. There, it is a conversation in a car (again a precise location) which is overheard by a blind man and a little girl as they're passing by.
It is this conversation which holds the key elements of the plot, but of course at the beginning of the film, it is encrypted for us. Just like the art gallery scene in "The bird", which only unfolds its secret at the very end of the movie.
There comes the founding scene of "4 flies on grey velvet" (1971), baroque, picturesque and surreal: One evening, a young rock musician, Tobias, follows into an opera house a man he suspects has been spying him for days.
What better place than an opera house could Argento choose to stage a tragedy?
The moment Tobias enters the building, he symbolically switches to a different world, which boundaries are physically marked by several red velvet curtains he passes through.
Outside is the real world. Inside is a parallel dimension, a vast and empty music hall in which light projectors focus the attention on the stage, where a fight between both men start: the prey becomes the predator as the musician accidentally stabs the mysterious man to death in a reflex of self-defence.
Sole audience of this scene, a third person takes pictures of the crime from the mezzanine. A person wearing a scary smiling mask.
This is the incredible talent of Dario Argento: in an almost exaggerated, maybe typically Italian way, he underlines a scene by making it stand out of the rest of the film, creating what could appear as a completely artificial rupture, yet totally convincing. Like if he was telling us: "Now look very carefully".
Paradoxically, it is when all the details are offered and pointed out that the mystery springs: by indicating where to look, Argento blinds us.
"4 flies on grey velvet" is a much more interesting film than what is usually said about it. Correspondences with David Lynch's work are quite intriguing and visual ideas are really ahead of their time. Check darkdreams.org for a detailed review.
It is however difficult to find a copy of it, as no DVD was released yet. You can still try your luck with second-hand VHS on eBay.