so at the end we saw Carl and Rick being bussy, and now im wondering where we are at.

there are 2 options though, we either get a ´flashback´ to the begining of the season through the Governor´s eyes and perhaps he did sabotage the prison by feeding the zombie´s the rats near the gate etc.

or that stays unsolved for now, if its not the governor then i still believe it was that little girl.

but seeing the situation, Hershel outside with Michonne, i´d guess its the 1st option