Melissa Suzanne McBride, Chad Coleman

[Warning: This story contains spoilers from Sunday's episode of The Walking Dead. Read at your own risk!]

The Walking Dead has never shied away from gruesome deaths and the horrors of being on the run in a post-apocalyptic world overrun by zombies. But the AMC series took its level of morbidity one step further during Sunday's episode.  

The Walking Dead: Who the heck was that?

Earlier this season, we saw that Lizzie (Brighton Sharbino) still believed that the walkers are people. In fact, Sunday's episode revealed her as the culprit who, while the survivors were still living at the prison, was feeding the walkers rats. That, of course, doesn't compare to that time she tried to smother baby Judith or how she was playing a game of tag with one walker. Suffice it to say, this little psychopath and her behavior had to go.

But it wasn't until Lizzie brutally stabbed her own sister Mika (Kyla Kenedy) to death — in order to prove that she'd come back to life and still be herself — that Carol (Melissa McBride) realized the severity of their problem. Much like the pet-turned-rabid dog Old Yeller, Lizzie was deemed a danger to others. Carol therefore took Lizzie out back and shot her in the head because no one would want this sociopath coming back as a zombie.

The Walking Dead's Michael Cudlitz on Abraham Ford: "He will kill you"

Over the years, the series has presented far more grisly and bloody deaths. Therefore in some ways, these deaths pale in comparison, especially since we're spared seeing the actual killings, which take place off-screen. What makes them particularly disturbing, however, is the fact that two uninfected children were killed -- one by that child's sibling and the other by a caretaker -- deliberately and with forethought. Lizzie was clearly delusional. But in the case of Carol, where does killing in self-defense end and murder begin? This situation parallels Carol's actions earlier this season when she burned two of the adult survivors sick with The Flu to death, so they wouldn't come back as walkers. In this world, you have to do anything and everything to survive, right?

Do you think The Walking Dead went too far? Hit the comments with your thoughts.

The Walking Dead airs Sundays at 10/9c on AMC.