I still wonder if the Zombie virus didn't save Carl. There's still the question of what happened to Rick during the advent of the Apocalypse. He may be a "living Zombie." And, since Carl is his kid, he may have the same genetic structure to allow that to happen.
There's still the question of what the CDC guy whispered to Rick. It might have been about the living zombie idea. Couldn't have been Lori's pregnancy since that came as a surprise to Rick.
Here's a brief and largely unenlightening article on the topic.
Lincoln said the message—which Jenner uttered right before committing suicide—should be revealed this season, and he notes it is "pivotal" for Rick.
"This is a scientist who seemingly held all the cards to what this epidemic is about, and I do think, you know, you would imagine he would have something of value to say on that matter," he said. "Well, he chose to kill himself."
Something about the zombie plague that is more upsetting than, yknow, just
the zombie plague part...hmmm...
I'm sticking with "You're already dead, and that's not a metaphor."