Alright, this is just another prediction about Season 4.
As seen within the Walking Dead Season 4 Trailer... Tyreese, Daryl, Michonne, and Bob were attacked by a herd of Walkers. After reviewing the trailer, I think that they were looking for a new Safe Haven therefore the Prison wasn't safe anymore. Well, I think they were coming back from the Farm, thinking all the Walkers moved on, EXCEPT!!! On there way back, the Walkers come out the woods and attack them as seen... Just a prediction, I don't know what'll happen... but I can't wait!!!