I am Rick Grimes' missing hand
OHHHH SNAP!!!

OHHHH SNAP!!!

The Walking Dead: A Decade of Dead

A Walking Dead Documentary

At the end, when Patrick dies, you realize that this is not an isolated incident. [Rick’s] pig is dead, we see the walker at the fence … it’s a ticking time bomb. Now, all of a sudden, [the virus is] right in the middle of the prison. We set up some great beats. Norman [Reedus, as Daryl] set up a great beat when he licks his fingers then shakes Patrick’s hand. You look at it and go, ‘Wait a minute, Daryl licked his fingers and shook Patrick’s hand and now Patrick is [dead].
Robert Kirkman on the Spanish Flu that is taking out the group
Pulling in a new threat in your fourth season, I think, is a good thing. Also, it’s important to know that this is really just some form of the Spanish Flu. It’s something that exists in our everyday world now; it’s a time where there is no modern medicine. Scott Gimple, the new showrunner, really wanted to explore that new possibility of the simple things, the really little things, coming to devastate these people. That’s what we’re going to explore.
Robert Kirkman on the new virus on The Walking Dead
Because he is amazing and very much fits the character. Abraham is a larger than life character that comes in and bowls over the characters. He’s just a take charge kind of guy and we need somebody that has that presence, that can stand up to characters like Daryl Dixon and Rick Grimes and really hold his own. This is a guy that can stand shoulder-to-shoulder with Tyreese and be imposing and that’s something that we needed and that’s something that Mr. Cudlitz delivers quite well.
We recently found out that Michael Cudlitz, formerly of Southland, will be playing Sgt. Abraham Ford. Walking Dead creator Robert Kirkman tells us why, in his mind, it’s a perfect match:

[Entertainment Weekly]
It is escalating I guess to a certain extent, but that’s because as the characters move further and further away from civilization, they’re going to start encountering more and more dangerous people. That’s not by accident. Things do get a little bit harsher. But it’s a violent world and we have to realistically portray that or people won’t buy this story. And to that, people gots to die, I always say. And they have to die in horrific ways. So it’s going to be pretty gruesome in some ways, but it’s always about character at its core. As long as we maintain the show’s humanity, I don’t feel that we lose our way.
The Walking Dead’s Robert Kirkman explains that this season’s going to get worse and worse for the characters:

[E! Online]

He’s definitely going to appear at some point this season. It’s possible there are elements of his return that have already been set up in some ways you might not have noticed. But when he returns it will be at a time when you least expect it.

I think that to a certain extent we will be exploring all characters more than we have. This show has been doing a lot of world-building for the first three seasons. Now that we’ve got that out of the way, this season we’re going to be intensely focused on the characters themselves. You’ll learn a lot more about Beth, you’ll learn a lot more about Daryl, you’ll learn a lot more about Rick. We’re going to be doing a lot of character work this season.

The Walking Dead’s Robert Kirkman talks about the Governors return. 
It’s a lot of what comes from that woman [in the woods] in the first episode: It’s “Aren’t these people too far gone?” And “Can these people retain a little bit of humanity?” We’re going to be dealing with those questions a lot more intensely than we have thus far on the show. It’s all about Rick coming from this place where he kind of went off the deep end in season 3. Rick feels like he failed at everything he was trying to do and so this is him trying a different path and seeing if he can make that work.
The Walking Dead’s Robert Kirkman says that the theme for the season has already been established by the premiere:

I sometimes am the loudest when it comes to let’s change things up and let’s make things different. We’re all of the mind that the television show is a different animal, so while we’re adapting these stories we do want to keep things fresh and new for the television audience just like it was fresh and new with the comic book audience the first time they read it, so I feel like those changes are important.

We’re doing some very new and interesting things with The Governor in Season 4, as you’ll see. … The new season is about the continuing progression of these characters and their lives, so while we’re still in the prison, it is a very different prison than what we’ve known thus far, and they have kind of built a little pocket of civilization within those fences.

The Walking Dead’s Robert Kirkman states that he’s a fan of changes, and he hints at what’s in store for the Governor this season:

More at the link. [Huffington Post]

It came from AMC. This is something we would all like to do. Robert [Kirkman] has always been interested in expanding the world and doing something quite different than what he was doing in the book. It won’t deal with any of the characters from the book or the TV series.
The Walking Dead’s Producer Gale Ann Hurd gave a few more details about how the spinoff came to be and what it will look like:

[The Hollywood Reporter]