- The book describes a story tainted by a Featureless Plane of Disembodied Dialogue as being like two brains communicating telepathically in a lightless room in vats of nutrient-rich fluid, then jokes that if that really is the setting of the story, carry on... but wouldn't you still need to know which brain was talking in a story like that?
- Depending on how the scene is done the reader might be able to follow by seeing which line comes first and picking up details of the speakers by the quirks of their dialogue. This would require that the writer of such a book be sufficiently talented that the quirks of the characters' respective dialogues would become immediately recognizable to the reader over time, and if they were that talented, they probably wouldn't need to read a book like How Not to Write a Novel in the first place.
- Plus, well, it's a quip intended mostly sarcastically.
Fridge / How NOT to Write a Novel