- Creator In-Joke: The guy Cave Johnson fires at the beginning for misspelling "station" as "statoion" is named Chris. This is a reference to how level designer Chris Onorati, better known as TMast98, accidentally made this spelling mistake on a sign, which started a joke of the team "firing" him whenever he made a mistake. This is referenced in the credits, when Chris's drawing has the word "statoion" with the extra "o" crossed out. Also, in Chris's office at the beginning of Chapter 3, the whiteboard says, "Chris if you erase this board again I'll make sure you get FIRED!"
- Development Gag: Mel was the name of an unused human character who, alongside Chell, was a part of the co-op campaign before they were replaced with ATLAS and P-body.
- Throw It In!:
- In the Propulsion Gel Pump Station, there's a point where you fling yourself to a control room with a collapsed wall. By accident, the hole didn't line up with the intended fling path, so you just landed on the railing of the catwalk right in front of it. Instead of fixing this, the developers added a voice line from Virgil saying that "Normally when people do that sort of thing, they just fly through the hole in the wall".
- There's an area where a large piece of metal truss falls from above without warning, and strikes a metal pipe on its way down, making an extremely loud noise that would give anyone a heart attack. Apparently it was never meant to be this loud, and even startled the devs every time. Instead of making it quieter or removing it, they had Virgil tell Mel, "Oh, tha that's meant to happen! Just to test your uh reflexes!"
- What Could Have Been: Mel was once going to visit "Aperture Leisure", as advertised in Chapter 1.
Trivia / Portal Stories: Mel