The unintended horror was magnificent and to a degree, a lot scarier than what the game had to offer. And this could only happen in a game – where we’re more likely to believe there are ghosts in the machine.
My story is that when I was first playing Half-Life 2, once I got into the plaza behind the first processing building, the bird models didn't load properly. Apparently in Source when models don't load, they're replaced with an error model consisting of 3D text that reads “ERROR.”
So in the middle of this scene of a boot stamping on a human face (forever), there's a Stalinesque statue in the middle of a plaza with giant glowing ERRORs circling, while people milled about, minding their own oppressed business. I hadn't played Half-Life 1 so I didn't know anything about the story, so I wondered if somehow the world was some Matrix style simulation and I was seeing a peek behind the curtain. I felt in way beyond my narrative depth—which of course was also farther than intended, since that's not part of the story at all. It was just a glitch.