Warning: "The Walking Dead" Spoilers Ahead!

"We can't go back, Bob."

Two different men said these exact words to two different Bobs, but both translated to the same thing: "Time to die."

In one corner: Cannibal King Gareth of Terminus, surviving the world of flesh-eating monsters by becoming a flesh-eating monster. In the other: Cowboy Rick Grimes of The Road, ready and willing to do anything and everything to keep his family and friends safe — including murdering unarmed individuals without blinking an eye.

In episode three of season five, "Four Walls and a Roof," Rick and his allies prove just how far they've plunged into the depths of darkness, brutally butchering Gareth and the other survivors of his cannibal paradise. But that bloody display of violence, exhilarating as it was, pales in comparison to the opening scene from episode eight, "Coda," the midseason finale.

The episode begins with an unusual kind of police chase: ex-cop Rick behind the wheel of a stolen cop cruiser, pursuing a fellow cop he captured just a few hours earlier. "Stop running," Rick tells the cop, Bob, over the car's radio. Bob does not stop running. So Rick runs him down, sending Bob flying across the pavement, landing with enough impact to break his back.

"It didn't have to be like that," Rick tells him, standing over battered Bob. "You just had to stop."

Bob begs for his life. He pleads for mercy, for another shot. Rick gives it to him — right between the eyes. "Shut up," he says to Bob's body. And then it's back to the business of saving his friends.

Rick's casual murder of an unarmed police officer speaks volumes about where we are on "The Walking Dead." There was a time when Rick struggled with putting walkers down. When he killed his first humans — a pair of shifty strangers named Dave and Tony — it was a big deal. It was a huge deal when Rick killed his first cop: Shane Walsh, Rick's best friend in a long ago world, and his deadliest obstacle in the current one.

These days, Rick doesn't bat an eye when he guns down a cop in cold blood. These days, it's just common sense; kill the threat, or let the threat kill you. He chooses the first door every single time, and looks back with no regrets. It's a huge shift for the character, and it's resulted in the most interesting status quo for the series since… well, ever.

Five seasons in, "The Walking Dead" has finally delivered on its promise of pushing good people past their breaking points, stretching their limits until there's nothing left to stretch. Some of the survivors still believe in hope and redemption — Tyreese, with his short-fuse temper and ridiculous muscles, is the closest thing this world has to a pacifist — but by and large, our heroes are the type of people who will shoot first and ask questions never, so long as it serves and protects their unit.

Finally, "The Walking Dead" has arrived at the heart of the matter, echoing the words of Abraham Ford: "The world needs Rick Grimes."

But at what cost?