I am not sure whether other people have thought about this as O know most watch it got entertainment, however I was thinking of the science. The only way to kill the zombies or walkers is to destroy the brain. Even though the show is now supposedly several years after the zombie apocalypse, there are thousands of zombies walking around. They are supposed to be dead and as we all know dead people will start decomposing, including their brains. The fact that they can walk and even tear apart stuff means that their brains are still alive, blood is still flowing and muscles are still functional, and can still bite. This is not really believable as the brain is among the first organs to decompose. If a few years, that is fine. However, to see so many zombies decades later is simply not possible.
In some episodes we can see zombies without the body and only the head hissing and moving the mouth.
The explanation may be that the zombie apocalypse was caused by super microbes which take over the dead body and specifically the brain and keep it alive. Or alternatively a more credible explanation from a scientific point of view, may be nanobots released into the atmosphere which are now in the bodies of all human beings and which are activated once the body dies and they take over.
I know this has been a slightly morbid post. However, I would love to hear your theories of you are a fan of zombie movies and still reading my blog.