Come on, haven't you ever wondered if it's scientifically feasible?
In some magic-based practices, the process of making a zombie is taken as fact. With the right mix of ingredients, a person can ingest the concoction and go into a kind of stasis (think SciFi long-distance space travel). The body’s systems would shut down to almost a halt, maintaining just enough to keep and element of life present (yeah, like a glowing pilot light on a gas heater). There is no doubt this is possible. Every time we undergo anesthesia for a surgery, we are quieting down conscious brain function, but maintaining autonomic function so our hearts still beat and we still breathe. With anesthesia comes a dulling of pain senses and the creation of amnesia when it is over. Of course, this wouldn't make for a real zombie, just a dead-looking person. The zombie would supposedly occur when you reanimate the person. In the case of anesthesia or even primitive mixes of powders, it wouldn't make a zombie, it would make an awake person after deep sleep.
These logistics aside, the problem with creating a zombie is the basic knowledge that when you shut down body functions to the degree that breathing is not detectable, then not enough blood is reaching the brain. Even if you reanimate a person by say CPR means, if the person has been without oxygen for enough a period of time, the brain functions will not reengage. You will have anoxic brain injury and a vegetative state.
Saying you reanimate a person’s body, in order for them to be a walking eating threat, they would have to have some of the brain functions in order to still move about. The concept of a zombie being directed by its master to do tasks is absolutely impossible. It would be like telling a person in coma to sit up on the edge of the bed. So, in the case of this type of “zombie” they would not be able to perform the functions of wandering the streets. They would also be mortal and able to be killed.
So, let’s conceive of some situations in which a zombie-type creature could be created. It would take a few elements. There would need to be severe retardation of brain function to the point that the person is perhaps at the mental level of a 2-year-old and therefore understanding of commands, but not understanding of whether these commands are fair or unfair, right or wrong. In order to get this unfortunate person to eat flesh, it would take a condition of pica. Pica is a condition in which a person craves things to eat that are not eatable, such as clay, metal, soil, and the like. Along with perhaps an ongoing iron-deficiency anemia, this lame-minded host could potentially be talked into cannibalism. In this case, at best, you’d get a docile child-like person who could be talked into eating flesh but would not have the natural tendencies to go out and seek flesh to eat. They would also be mortal and easily killed.
Other considerations: There is a disease called Kuru. It attacks the brain in a sort of mad cow disease type of way. It was found in New Guinea to be caused by cannibalism and the eating of the brains of those infected. This disease kills usually within 12 months and is also called the “shaking” disease or the “laughing” disease because it causes uncontrollable shaking and outbursts of laughter. That would make for a much different zombie, as this one would walk and talk, but also shake and laugh uncontrollably. Probably not that threatening. They would also be mortal and able to be killed, but would die on their own within several months in an agonizing manner.
The true zombies of pop folklore are an interesting concept, but the reanimation of flesh would also include an anoxic body that would not be able to have a brain function to move about, think, desire to eat, or any other features we’ve come to know.
Just because zombies can’t physiologically exist in the manner shown in movies presently, there are other aspects of medicine upcoming in the field right now that could change the present impossibility. Doctors are working on a kind of patient stasis that would keep their body functions on the lowest level of existence until they can come up with cures for what ails them. This is different than “putting a head on ice” cryogenics. Still, these two forms of putting people in stasis and then reanimating them could very well create conditions we aren’t aware of. Certain parts of the brain could feasibly be revived while others die off creating an imbalance in behaviors and tendencies. This might be like a football head injury can make someone suddenly very angry when they were kind before. Still, this would be a mortal condition and able to be destroyed.
Ultimately, the only true flesh-eating, killing, ruthless, nearly indestructible zombie you could ever invent would involve some very savvy Japanese engineers. It would have to be robotic. This could be programmed in many ways and the thought is actually a bit more chilling than flesh and blood, shoot `em in the head zombies.
Whether zombies exist in the future or not, the concept of a person dead but walking, alive but soulless is one that continues to fascinate and repel.