The Cat o' Nine Tails is a 1971 giallo film written and directed by Dario Argento. Although it is the middle entry in Argento's so-called "Animal Trilogy" (along with The Bird with the Crystal Plumage and Four Flies on Grey Velvet), the titular "cat o' nine tails" does not directly refer to a literal cat, nor to a literal multi-tailed whip; rather, it refers to the number of leads that the protagonists follow in the attempt to solve a murder. Though successful in Europe, it was dismissed in the United States. Argento admitted in the book Broken Mirrors, Broken Minds: The Dark Dreams of Dario Argento that he was less than pleased with the film. In fact the director often cites it as his least favorite of his films.
(Summary from Wikipedia)