Gialli's plots explanation or resolution often hides within one key image.
In "The bird with the crystal plumage", it's a painting - bought in an antique shop - which reflects the initial trauma experienced by the murderer.
"The bloodstained shadow" also revolves around a painting which depicts the terrible truth behind a scene the main character was a witness of when he was a child, and that he could not remember in details.
It's a photograph that reveals, when blown up several times, a murder was committed in Antonioni's "Blow-up". A similar treatment applied to a newspaper photograph (by the way, how unrealistic given the usual quality of pictures in papers!) unveils the secret behind the scorpion cuff links in "The case of the scorpion's tail".
We could also mention it's the re-cropping of a photograph which shows that what initially looked like an accident - a man falling under a train in a railway station - was indeed a murder in Argento's "The cat o'nine tails"...
Paintings or photographs, Giallo marks the victory of the visual and symbolic approach over the narrative, litterary explanations which used to prevail in "classic" thrillers up until the late 60s.
In this instance, it illustrates this genre's modernity, reflecting the movement towards the image-based society we all know now.