Zombies almost always eat human brains. That cries out for the question, how do they digest them? In order to get any nourishment from brains, the monster needs a digestive system. That implies a working respiratory and circulatory system to distribute the brain energy to all parts of the zombie. And, if they do not have these systems, what is the use of eating brains? In the fulness of time, the zombie would fill up and be unable to physically pack any more brain down. And poop. If you eat, you must poop. I think that is the Second Law of Digestivity. The whole idea of zombie poop is disturbing. You can bet they would not clean up after themselves. So either these guys have functioning digestive, circulatory, and respiratory systems, and are thus only a short way from just being ugly guys; or they have none of that and it brings the whole brain eating habit under suspicion.
It’s something to think about.