- The gap has been long enough between Episodes Two and Three that Actor Existence Failure has begun to take hold, with Dr. Breen actor Robert Culp having passed away in the interim (thus becoming unavailable for any potential flashbacks, recordings, backstory cutscenes, etc. that Valve didn't get around to recording when he was alive.
- Talking to Himself: There is only one voice actor each for all male and female rebels. Any time two same-sex rebels have a conversation, it's with the same voice. Episode Two added a second voice actor for Sheckley since he was specifically written to converse with Griggs (who is voiced by the same guy as the other male rebels).
- Done in-game during Point Insertion, as one man paces in front of the arrival/departure board repeating worries about the trains and disappearances. It's quite clear he's not talking to anybody but himself.
- Throw It In: In the development of Episode 1, one of D0G's default animations played inadvertently during a scripted scene. It was so fitting that they hard-coded him to do it and wrote Alyx's dialog around it.
Alyx Vance: Well, Gordon... unless you have a better suggestion... He is a robot. He's done the math.Alyx Vance: *to D0G* You did do the math, right?*D0G sheepishly shakes his head*
- What Could Have Been: Numerous things were cut from the game, including new weapons, old and new enemies (the Bullsquid and the Cremator, respectively), and story elements that made the world even more horrible than it already was.