Movie plot device: The Background Squealer

Last week, lissener and I got to take in Dario Argento’s The Bird with the Crystal Plumage (IMDb) in a rare big-screen showing. This early giallo features an American writer in Rome who witnesses an attempted murder, and winds up entangled — first involuntarily, then increasingly by his own foolhardiness — in the investigation. It’s a pretty good movie, even though the production values are sometimes shaky, especially the looped soundtrack, and the fact that it was made in 1970 leaves certain aspects fairly dated.

Which brings me to the main question: One of the primary clues in the investigation is a recording of a phone call in which the killer apparently contacts the witness to taunt him. Midway through the call, in the background underneath the killer’s voice, an odd sound is briefly audible. Naturally, the police focus on this sound, because if they can figure out what it is, they may be able to identify where the call came from. I won’t say anything else, because I don’t want to give anything away for people who intend to see it; the film is a must-see for Argento fans. (“So long!” heh heh.)

But of course, at that point, I started thinking about every other film in which the overheard sound has played a role in the plot. There’s that bit in The Fugitive, I vaguely recall, where the Tommy Lee Jones character is able to determine that Harrison Ford is using a phone close to a certain railway station. And in the underrated Bill Murray comedy Quick Change, the cop played by Jason Robards Jr suddenly understands the bank robbers are no longer in the bank based on the quick beep of the horn when Randy Quaid accidentally bumps it while Murray is on the phone. There are lots of other movies in which this device makes an appearance.

I can’t think of any examples prior to 1970, though, and I’m wondering if this plot device is original to the Argento movie (and the source of all the subsequent ripoffs) or if somebody used it before Argento did. I’m racking my brain, and I can’t come up with anything. It would be nice to know whether Argento gets the credit for coming up with what is now a well-worn cliche (which, in the tradition of Ebert’s Little Movie Glossary, I’m calling The Background Squealer per the thread title), or if he swiped it from somebody else.

By the way, I should also mention that according to the IMDb, The Bird with the Crystal Plumage is adapted from a novel, but I can’t say whether the plot point in question comes from there or not. However, considering that the novel was written in 1948, and based on the plot information available in the book’s Amazon entry (not to mention its prior film adaptation), which suggests a loose connection at best with the later Argento movie, I’d say probably not.

Can anybody think of an earlier usage of this plot device?