In theory, litmus strips should be touched against a character in order to operate, and may take some time to register; presumably they would then change color to indicate whether or not a character is a Mary Sue or a canon going out of character. In practice, they have a tendency to ignite even within their protective containers when exposed to particularly offensive violations of continuity or characterisation. Such burnt litmus strips smell bad, but at least they don't explode. Most of the time.
Litmus paper has largely been superseded by the various CADs, which can provide exact measurements from a long range. As a result, the use of litmus strips has been uncommon as early as the Original Series. Agents who repeatedly destroy CADs at a faster rate than normal, or are planning to enter a badfic where a CAD's detonation is a given, may elect or be elected to use litmus strips as a temporary measure.
- "Two Worlds" (The Lord of the Rings x Harry Potter), Agents Jay Thorntree and Acacia Byrd (DIC)
- Jay and Acacia decide to use litmus strips instead of replacing yet another CAD.
- "The Dark Elf" (The Lord of the Rings), Agents Jay Thorntree and Acacia Byrd (DMS)
- Jay and Acacia use a litmus strip and detect extreme OOCness without even touching the character.
- "You Now Have 46 Hours," Part 1, Part 2 (Sherlock Holmes), Agents David Kelok and Unger (APD)
- Kelok and Unger use litmus strips in part 2.
- "Ring Child" (The Lord of the Rings x Harry Potter), Agents Supernumerary and Ilraen-Aroline-Fothergill (DIC) with Agents Suicide and Diocletian (DMS)
- Suicide and Diocletian use bootleg litmus strips during an evaluation while they aren't allowed weapons or PPC gadgets. Most of the strips fry in their container.