Naughty Dog's seemingly gone mental with all of this tech in The Last of Us: Part II. In an interview with Polygon, co-director Anthony Newman explains the game's "heartbeat" system, which sounds equal parts insane and impressive.

The gist of it is that in The Last of Us: Part II, every character -- that's Ellie, her allies, her enemies, the infected, everyone -- has a "heartbeat". When characters are performing strenuous actions like running, jumping, and engaging in combat, their heartbeat increases, and this leads to dynamic audio like heavier breathing and panting. Yeah, we told you that it sounds crazy.

"I’m not sure if you noticed it, but as Ellie sprints around and then she settles, she’ll kind of [mimics heavy breathing] catch her breath," Newman says. "What’s happening behind the scenes is that [Ellie] has a heart rate that is oscillating up and down. It goes up when you sprint, it goes up when you melee, it goes up when you take damage, and goes up into the presence of enemies. And that modulates the bucket of breathing sounds that she’s able to use."

But again, this same system applies to enemies as well. If foes are looking to quickly sneak around the back and flank you during a skirmish, then you might hear them coming, especially if they're already knackered.

"It’s been incredible because I found myself able to play cat and mouse with Clickers better than ever before because I can kind of understand them by the noises that they’re making," Newman teases rather creepily.

What do you think of details like this? Don't break your immersion in the comments section below.