When people talk about Call of Duty 4, the game created by Infinity Ward and released in late 2007 by Activision, they usually refer to its longevity in sales and in multiplayer action or to its bold attempts to insert a meaningful story with tough moments in a top of the line first person shooter.

But one aspect crucial to the success of Call of Duty 4: Modern Warfare was, according to one of the people who worked on it, the way it managed to “put dirt in the right places.”

Michael Boon, who was the technical art director on Call of Duty 4, says that adding dirt to the characters, especially during cut scenes and other moments when they are under close scrutiny from the players, helped Infinity Ward create some pretty real characters, which did not suffer from the “uncanny valley” issues that most modern videogames generate, by creating characters striving towards realism in their looks but appearing to the player as being stiff and inhuman.

Boon said that “I think the trick to gradually traversing it is to focus on going as far as you can with the character model itself. Then look at ways to enhance that model with improving elements affecting it - such as the lighting, self-shadowing techniques, and other ways to improve not just the model itself but how it's viewed naturally in the world.” Then, it was all down to throwing some dirt at the models. The technique proved so popular that the development team needed to be persuaded to create a less dirty look for the various characters making an appearance.

With Modern Warfare 2 scheduled to be released this year, it will be interesting to see how technology has influenced the presence of dirt in the series. If the game is really set in Cuba and Vietnam, notoriously rainy places, then we might get to see quite a bit of dirt.