Let's take a pseudo-scientific approach to the question of - Can zombies bite through denim?
Anyone know how long its been (in TWD world) since the pilot?
I'm guessing about 1yr. I know that's not enough time for a human to fully decompose in less than optimal conditions. The zombie's are clearly decomposing though. However, this mystery virus re-animating them is probably pumping adrenaline like blood making the zombies unnaturally strong and the added benefit of no pain receptors. We've also seen how easily the zombie flesh and muscle tears and skull can be penetrated. All because of the aforementioned decay process.
Given these facts: unnaturally strong, soft bones, loss of elasticity in skin and loss of tensile strength in muscles.
My hyposis is: The older the zombie the less able to move or feed.
Therefore: The prison zombies should pose almost no threat. They should be barely able to stand. Their lower jaws should hang open or have fallen off. Either way not have the PSI to tear through denim.
But this is a fictional world and that would be boring to watch. Carry on.