Jack Palance was originally hired for the role of "Mr. Brown", but after clashing with the producers, he left the production. Before leaving he recommended they hire Richard Conte to replace him, which they did.
In what is arguably this film's most memorable scene, the weapon with which Richard Conte's character so effectively bludgeons Cornel Wilde's protagonist (albeit unbearably - and unforgettably - hearing-aid-enhanced), is the uncredited, offscreen contribution of the then hugely popular L.A.-based jazz ensemble, Shorty Rogers and His Giants; and in particular, the excellent but - in this case - literally deafening drum solo of Shelly Manne.
One of the very first American films to imply that women derive pleasure from receiving oral sex. The woman in question was actress Jean Wallace who insisted that the scene be shot when her husband (and one of the film's co-producers) Cornel Wilde wasn't on set that day. Wilde was not best pleased with the scene, blaming director Joseph H. Lewis for taking advantage of his wife. Nevertheless the scene now lives on as an iconic example of the cinema breaking taboos.
The film was considered very daring for its time. Cornel Wilde's detective character is clearly having a casual sexual relationship with Helene Stanton's Rita, while the film quite openly infers that the two henchmen played by Lee Van Cleef and Earl Holliman are in a homosexual relationship.