Yeah, I didn't really understand what they were hinting at with the two unbitten sheriff zombies, but it was obviously important because they bothered to point it out several times. I think that theory about Shane having immunity might be right (because didn't he get scratched when he and Otis were at the school or something
Also, did anyone get the importance of the lone walker in the field that Shane sees on the way there and on the way back? They spent too much time on it for it to just be meaningless. I thought that maybe it was foreshadowing walkers coming to the farm, since it was walking the same direction they were driving when they were going back?