-- Trail off (leave the reader to connect the dots)
-- Say nothing (do all of the above)
This was a slide from a writers' workshop Arianne "Tex" Thompson gave in Austin in July of 2017, titled "The Plate Tectonics Theory of Dialogue". It looked at dialogue through the metaphor of plate tectonics: your characters are constantly in motion, constantly changing. They clash, collide, fold, buckle, shift. Good dialogue expresses all that.
This followed the discussion of bad dialogue from the previous picture.
In the workshop we examined two pieces of dialogue from the television show "The Wire", both about 1.5 pages long. "Tex" Thompson praises this show for very good dialogue. We examined how the characters in those two scenes do all of the above: add depth to the characterization, emphasize, evade, understate, leave the reader to connect the dots, all the while speaking like believable, real-life people.
This is a second workshop by Tex Thompson that I have been to. The first one was the "Escape from Clichea" fantasy worldbuilding workshop that Tex Thompson gave at ArmadilloCon 2016 (a local science fiction convention). I found it very helpful, entertaining, and full of practical, doable advice. Here is my blog post on Tex Thompson fantasy worldbuilding workshop.