Humour comes in short supply in Giallo.
Four flies on grey velvet (Dario Argento, 1971) is a notable exception. If the main character, Michael Brandon, is quite a bland figure, secondary casts are an interesting gallery of tragi-comic characters, sad and grotesque in a unique Italian way.
Take Gianni Arrosio, for example.
Played by Jean-Pierre Marielle, one of the finest French actors, Gianni Arrosio is introduced to us as a homosexual private eye who never solved a case in his life.
Even though Argento's vision of homosexuality is highly stereotypical and sometimes falls into a caricature, Marielle manages to turn it into some kind of weirdness which gives Arrosio an amusing bizarreness.
When Tobias, the rock drummer who's blackmailed for a murder he committed by accident, comes to meet him, Arrosio is busy re-painting his office, wearing a ridiculous blouse. Taken in this embarrassing situation clearly showing he's got nothing much to do, he doesn't seem surprised and very naturally puts down his brush to sit back at his desk, ready to listen to his new client.
"After so many failures, the probability of me solving this case has never been so high", he says as an encouraging start for his investigation, leaving Tobias puzzled. From the very start, Marielle makes his character a tragic clown, both funny and desperate at the same time.
Later in the film, Gianni Arrosio will be the first to identify who's behind the plot. When the blackmailer leads him into a trap in Milan subway's public toilets, and eventually kills him by injecting air through a hypodermic needle in the heart, his last words will be: "I knew I was right". As if he could not believe himself that a success would be possible.
Such an achievement could only condemn him to death.
Jean-Pierre Marielle is an actor whose talent is unique. More about him on Wikipedia in English or in French.