I may be alone in this, but I believe that
Randy is who helped
Michael out of the Waterworks, and has been a zombie the entire time (well, since zombies came around, at least..). We've established that there are "smart zombies" that seem to be in control of the hordes...what's to stop some smart one from being sentient enough to control their own impulses, most of the time? I tend to think of Randy (and potentially, those like him) as a vampire like creature. In control most of the time, but every once in a while, just NEEDS to feed.