There's a famous half hour segment in Uncharted 2 that never fails to raise a smile.
Nathan Drake, still recovering from a previous show-stopping dance with death, is now hopelessly following a Tibetan explorer named Tenzin into a twisting cave blanketed with snow and icicles. As you pass through the gaping monstrous mouth of the cave's entrance, you enter a dazzling labyrinth of crystal-blue ice. Clearly, getting around will be a challenge.
So Drake, following Tenzin's lead, will swing across perilous pits with old rope, dash across crumbling ice bridges and, as a reward, will be attacked by a terrifyingly fast Yeti-like creature.
Throughout it all, you and Tenzin form a special bond - the kind that can only be forged when two people begin to rely on each other to survive. What makes this connection so special and charming is that neither Drake nor Tenzin speak the same language.
Over the past 40 years, video games have swung from outright neglecting dialogue (Doom, Sonic et al) to employing the spoken word with the elegance of a sledgehammer to a door. In 2009, when Uncharted 2 hit, few expected a game so sophisticated that it hinges success on guessing what a Tibetan is saying.
Neil Druckmann, creative director at Naughty Dog, appreciates the complement but isn't revelling in the success of the Tenzin chapter.
"That whole scene completely ripped off Ico," he says, jokingly at first (I think), before discussing Fumito Ueda's breakthrough game with gradually escalating levels of passion.
"Ico was, wow... it was pretty incredible. It was fantastical but believable; all of its architecture had an internal logic to it. Actually, to be honest, it was one of those things that got me into the games industry.
"But the main thing I loved about Ico was that relationship; that hand-holding mechanic that helps build a bond. It was the first time I realised you can create something meaningful through interaction, as opposed to just telling a story."
Late in 2009, amid the rapturous critical and commercial successes of Uncharted 2, Sony approached Naughty Dog with a proposal to expand the studio into two teams. One group would work (nay, crunch) on Uncharted 3, while the other would create something entirely new.
Suddenly, that thirty minute jaunt in a perilous ice cave took on a new significance in Naughty Dog's history. Druckmann's team decided to build a whole new game based on that central concept of two characters relying on each other. Three and a half years later, that project would be set for release worldwide under the name The Last of Us.
"We felt we had scratched the surface with that Tenzin scene, and we felt there was just so much more we could do with it," Druckmann says.
The Last of Us has already achieved notoriety for its army of mutilated fungal-infected humans, its panicky 28 Days Later vibe and its intentionally appalling scenes of violence. But Naughty Dog wants its latest project to be remembered beyond those talking points. As much as Druckmann describes Ico as this legendary game built around a bond between two characters, the truth is he wants to match that achievement.
"The Last of Us was always about Joel and Ellie. Everything is Joel and Ellie," he says.
"Even when we didn't have the genre locked down, even when we didn't know this was going to be survival horror or survival-action, we knew this game was going to be about two characters."
Players will assume the character of Joel, a survivor of the plague now in his 40s, who traffics drugs and weapons through quarantine zones. At some stage in the game's opening story arch, he will meet Ellie; a fourteen year-old orphan who was born into the plague era and knows no different from it.
It's not the smoothest collision of destinies. In fact, Joel and Ellie couldn't be more ideal candidates as strangers to each other. Yet as they progress through the story, under your guiding hand, both begin to learn from one another. As time passes they begin to understand each other. Eventually they begin to rely on one other.
"Our priority was portraying the development of that relationship," says Druckmann, who can see the incomprehensibly complex AI network hidden behind Ellie to make her appear real.
"If Ellie ever comes off as annoying, or not human, then we will have failed. Everything depends on the player growing to like that character."
He said one approach is allowing the player to witness Ellie's personal growth throughout the game. At the outset, Ellie can barely whistle, but over time she develops a pleasant and gradually familiar sound. It's one of many things Ellie will do if left to her own devices. She'll constantly walk around rooms and observe objects, and every now and then will call you over to talk. The objective is to make these rigid tasks appear natural.
"During development I was waiting for someone from Sony to come in and say, you have to cut this from the game. But they backed us all the way."
But if building a believable human character wasn't overwhelmingly complex enough, the recent release of BioShock Infinite has moved the finish line even further up the hill. Irrational Games' intelligent and enthralling FPS has single-handedly changed what audiences expect from sophisticated AI companions. Elizabeth was perfect, and there's no way I could leave the interview without asking Druckmann whether he feels pressurised by that.
"Honestly, we don't try and think about what other people are doing," he says.
"We just have to keep on focusing on our own work. Our focus is to make sure everything seems evolving and organic."