Artistic interpretation is, in some respects, always subjective. Many things in our realities depend on our perceptions but there are some things that are true regardless of whether or not we believe or recognise them, things like murder. But in Dario Argento's 1970 giallo film The Bird with the Crystal Plumage (L'uccello dalle piume di cristallo), stopping a serial killer is dependent upon one man's perspective. It's a film that effectively builds terror and suspense from the protagonist's attempts to find the right interpretation in time to save the next victim, each one of whom is killed in the gory and slightly eroticised fashion one might expect from giallo.
All of the victims are beautiful young women and in one case the killer slices off the victim's clothing before killing her, which would seem to indicate a sexual motive. In the first attack we witness along with the protagonist, an American writer named Sam (Tony Musante), another beautiful young woman is in danger of getting slashed.
Sam witnesses the scene through a glass front of a brightly lit art gallery, the rectangular portal of bright light in the darkness, separated by an invisible barrier, is conspicuously reminiscent of a movie screen. The fact that it's an art gallery further emphasises the need for interpretation.
Becoming trapped in the entry way between two glass doors, Sam is both helpless to intervene and unable to leave and call the cops. He catches the attention of a passer-by who phones the police and the woman manages to survive despite a bloody gut wound.
Sam is only briefly a suspect but he becomes obsessed with finding the killer anyway. He befriends the chief inspector who lends a few officers and the crime lab to assist Sam. There was something strange about the scene, Sam says, something off that he's missing and he replays it over and over in his head, certain he'll be able to find the killer when he realises what it was.
The fallibility of Sam's perceptions manifests repeatedly in the film. He and his girlfriend (Suzy Kendall) are at one point pursued by a gunman in a yellow coat. When they get to a public area and Sam tries to pursue the gunman, he chases the man into a pugilists' convention where everyone is wearing identical yellow jackets.
When he learns the killer was obsessed with a particular work of art, he and girlfriend study the painting looking for some clue. It looks slightly like Bruegel's The Hunters in the Snow but with a murder.
Eventually Sam tracks down the artist himself who offers Sam dinner, meat the nature of which Sam finds he has misinterpreted to his disgust and chagrin. The killer makes calls to the police and to Sam and in one case an unusual sound can be heard which the police and Sam endeavour to recognise to no avail. Even the seemingly omniscient crime lab computer doesn't recognise it.
The movie has plenty of red herrings and several characters seem plausible as being the killer's true identity. But when the revelation comes, it's possibly the most interesting choice and one that serves the film's ideas nicely.