Remember the first time you clapped eyes on the facial animations Valve created for its Half-Life 2 characters? It was awesome, stuff we'd never seen from a videogame previously and in this regard stuck a boot up the arse of 'real' and kicked the game way over the heads of the competition.
But such animation is only part of the trickery behind the face to create believable in-game characters.
In order to keep NPCs real, Marc Laidlaw, Valve's Half-Life plot man, has explained the developer tries to draw strong relationships between the characters, and that making each one part of a believable network of family and friends (and rivals) makes it easier for players to relate to them.
"Characters in weaker science fiction stories often seem flimsy because they're solitary heroic figures without parents, siblings or ordinary relationships", he said in an interview with PC Zone magazine.
Character-driven drama depends on social context, status transactions, how they relate to other people in the world, explained Laidlaw.
"We also assume our characters have spent their whole life in this world - especially Alyx, who grew up surrounded by headcrabs and Vortigaunts."
These characters, Laidlaw said, are drawn in such a way that "the crazy SF details" that populate the Half-Life universe are just ordinary, everyday obstacles to them. They're obstacles still full of potential threats and surprises, as in our own world, "but with a grim internal logic".
You can read the full interview with Marc Laidlaw on these pages shortly.