One thing I was wondering is... Was the zombie that was laying against the wall & bit Herschel faking it? In otherwords, was it a trap the zombies had set? If the zombies are getting any sort of intelligence, then this show could go to a whole new level of awesomeness.
Maybe he wasn't, but it just seemed odd that all the zombies had disappeared, and suddenly this zombie was just laying there, waiting for someone to walk by. He didn't hop on Hershel when he saw him, rather he waited until he was almost completely passed before he chomped down on his leg. And at that moment, the entire horde of Zombies rounded the corner and began chasing everyone again after they had all but disappeared.
Could be way off, but it's something to think about.