This should go without saying, but SPOILERS AHEAD!

The prison was not a very good place to be this week on "The Walking Dead," as Rick Grimes and company were attacked by Walkers from both outside and inside the walls of their so-called sanctuary.

A lot of extras were killed off, we got insight into one of our lead character's backstory and we said a pretty shocking goodbye to a familiar face.

Keep reading for 5 takeaways from "Infected."

1.) This Virus Is As Big a Threat as the Zombies

This week, the mystery flu that claimed poor Patrick also took the lives of 2 additional survivors. With the virus spreading, everyone's in danger -- because even one zombie inside the prison walls can lead to an outbreak.

Which is exactly what happened. Zombie Patrick turned Cell Block D into a war zone, and almost everyone in the entire ward was killed off pretty horrifically. This virus isn't going away soon -- and there's even a new doctor character on the show now to help the survivors deal with it.

Interesting to note that Patrick passed Karen's cell before snacking on someone else. Could he sense she was already infected?

And speaking of Karen, we had a feeling she wouldn't make it out of the episode alive after it started with some sweet, intimate moments with Tyreese. That's always a bad sign. But what a way for him to find out she was gone -- instead of delivering his sick girlfriend flowers, he found her burned corpse.

Someone's going to have to pay for that next week.

2.) We Smell a Rat!

At the beginning of the episode, we saw someone was feeling the walkers rats. While we don't have the culprit's identity yet, we're leaning towards little Lizzie -- who not only considered one of the zombie's her pet, but was also described as "messed up" by her own sister.

Whoever is feeding them is causing some major problems for the survivors though. There are more walkers than ever outside the gates -- and the horde was almost successful in taking down the wall. 

So Lizzie, if it's you, stop!

3.) Carol's Getting More Screen Time -- And It's Awesome

Carol is taking a more central role this season and we couldn't be happier. Her character has one of the more interesting storylines going right now.

Last week, we saw her giving survival lessons to all the kids in the prison -- but was keeping it a secret from both Rick and the kids' parents. This week, Rick found out, but he's going to allow her to keep doing her thing.

While we applaud her for doing this (she, more than anyone, knows the children need to be prepared), talking a young girl into putting a knife through her dead dad's skull is a little cold. If she's going to be Lizzie and her sister's new mom, she may need to get some of her compassion back.

We're pretty sure that'll happen ... but when will she get it on with Daryl?!

4.) Officer Rick Grimes Is Back on Duty

Rick had been living a low-key life at the prison, trading his gun for a gardening hoe. In an attempt to make life somewhat normal for him and Carl, he had sworn of his weapon and took his son's gun away too.

But that peaceful existence could only last so long in the zombie apocalypse.

This week he was forced to sacrifice his prized pigs to get the horde away from the collapsing prison walls. This was a clear sign his farmer days were done and at the end of the episode he strapped his holster back on -- and gave Carl his gun back as well.

5.) Michonne Has a Heartbreaking Past

The most gut-wrenching moment came midway through the episode, in a scene with Michonne and little Judith.

While the katana-wielding warrior was getting bandaged up by Beth after twisting her ankle, she couldn't stand listening to baby Judy's cries. After the infant threw up on Beth, she handed her over to Michonne, who wanted nothing to do with her.

But then, as she held onto the baby and looked into her eyes, Michonne broke down. Danai Gurira's performance here was devastating -- and it became clear the show's fiercest survivor lost one of her own children before joining Rick's camp.

Next week, it looks like Tyreese will be out for blood. Who do you think burned Karen's body without telling him?! And who's feeding the walkers? Sound off below!

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