My radioactively-reanimated zombie costume from last Halloween.
When fans are faced with the temptation to overanalyze, quantify, and contextualize fictional elements to see how they would "work" in the real world, the best advice comes from some philosophers who said:
"Just repeat to yourself, 'It's just a show, I should really just relax.'"
On the flip side of this, creators of fictional worlds should resist the temptation to explain too much, because the more complicated things get, the more potential inconsistencies you introduce. And when you go to the well too often (generally to fill screen time), you run the risk of watering down your creations, or otherwise make them look silly.
Two prime examples of this: The Borg were great as inexorable, unstoppable, relentless future cyborg zombie-surrogates, but when they started being the go-to Villain of the Week on Star Trek, when they started getting bogged down by nanoprobes and unimatrices and technobabble, and because they kept getting beaten, they stopped being really scary (thanks a lot, Voyager).
As to explanations making you look silly, one word: Midichlorians.
Zombies Don't Much Care for the Laws of Thermodynamics
The world of Max Brooks' zombies (in the Zombie Survival Guide and World War Z) is especially susceptible to all this, because it's written in documentary-style and aspires to something approaching reality. And the closer you look at the pseudoscience of zombies, the sillier it gets.
For example: The zombie virus ("Solanum") is bloodborne and 100% communicable at even the most minute levels ["...even one organism is enough to begin the cycle", ZSG. p. 4]. It's also 100% effective (that is, you're guaranteed to be killed and reanimated as a zombie -- additionally, if you eat zombie-virus infected flesh, it's 100% lethal, though at least you die and stay dead).
Because it's so transmissible, the entire human population would probably be zombified simply due to mosquito bites. To prevent this, in Brooks' world, parasites which might otherwise act as disease vectors instinctively "know" not to attack the infected.
Forget sniffer dogs to screen refugees -- you could check people by having them stick their arms in boxes of mosquitoes.
(Incidentally, the Zombie Survival Guide mentions that there are no documented cases of people having sex with a zombie, so it's left unclear as to whether the zombie virus can be sexually transmitted. It's likewise unclear if an infected carrier can spread the virus via sexual intercourse, though the other dictates of the universe suggest so.)
As to the rest of it: To his credit, Brooks' characters readily admit they don't know why zombies are able to do what they do. Brooks' zombies resist bacteria, so they don't really decay -- they abrade. They freeze solid in winter, but revive when thawed. They're immune to high pressures at the bottom of the ocean. They eat freshly-killed flesh, but they don't get sustenance from it -- they just do it because they are jerks.
Given that last bit, Brooks' zombies also don't care much for the laws of physics, since they are perpetual motion machines -- they produce work without requiring fuel. Put them on one of these power-generating walkways, and you have cheap, sustainable, non-greenhouse-gas-emitting undead energy.
The Point of All This?
As with many elements in popular fiction (especially science fiction), so to with zombies: It's best not to ask too many questions -- just suspend disbelief, and no matter how implausible the plot mechanisms might be, as long as they're internally consistent, you can just sit back and enjoy the ride.
(I'll save the Reaver implausibility discussion for some other time.)
Next time: Crunching the Zombie numbers.