Different Lies To Find The Spy

"Jenny: Undercover cops started nosing around old Dr. Brinkmeyer. I think they were lookin' to see if he was part o' that terrible racket o' fake prescriptions for weed that we all been hearing about.  Girl: But Brinkmeyer's not the one handing them out is he Jenny? You told me - Jenny: Yes, told you different. And I told you to keep quiet about it. In fact, I told exactly one of you the name Brinkmeyer, and that person was supposed to keep mum about it too. Ain't that right, Stevie?"

- A Young Girl's Delinquency Record Someone is a spy. But how to find them? This trope is about one solution. Tell multiple people different related similar lies, and then see how the person the spy works for reacts.

Fan Works

 * Jenny does this in A Young Girl's Delinquency Record.

Live-Action TV

 * Tyrion Lannister determined that Pycelle works for Cersei this way in Game of Thrones

Western Animation

 * Tina Belcher did this in the Bob’s Burgers episode Tina Tailor Soldier Spy