Ok, let's think about this. Re-animated corpses. How's that gonna work? I'm going to assume the heart doesn't restart, so we're talking about strictly anaerobic movement of the muscles. We're going to consume fat and then muscle mass as we go. Whatever is driving this train is going to have a very short life span on each host body.
It's going to have to hijack the nervous system, isn't it? That will allow it to move the bits and pieces around. Will the muscles pull the energy from where they need it? I'll need to check that out. Otherwise we have to restart the heart, and I don't really want to do that. I want a very short duration. Sure, without the digestive system, we can probably get the same effect, but I'd rather not have the blood pumping. We'll see.
I want it to be sentient, whatever it is. A parasite that rides chordate nervous systems. Does it get to access the memories of the host? Dunno. Does it get the muscle memory and coordination? No! Zombie shamble, dammit. It might be pretty good at faking it, especially if it has to go from host to host quickly. It'll be pretty used to learning to drive a new car, as it were.
How does it move from host to host? Well....contact with, well, brains would be great. But I don't think so. I like the idea of disembodied entities, waiting to inhabit the dead host. I'm not sure if I can make that work, though. I made need some sort of physical transfer. One rule is hard and fast tho-they can't attach to a living nervous system. The host has to be dead for the transfer to take place.
So, how do they reproduce? I have no clue. Shelve that one for now.
Where do they come from? Well, fortunately, this is a sci-fi zombie story. Humans travel to another planet. Very earthlike (but not so much so that they can breathe the air...that's dumb...sorry, pet peeve), eerily so. I like the idea of everything looking so normal that the environment suits the humans have to wear will look really creepy. There's an ecosystem devoid of primates or any tool-using, sentient life. Alpha predators-fearsume buggers with all kinds of weapons at the top of the food chain. Rabbit-things. Herd critters. Largely familiar creatures. Don't describe ANY of them as being like any terrestrial creatures. Niven fucked up with the Kzin. Tiger-like became "tigers" in every reader's mind. Don't go there. Except for the rabbit-things. We want the association that comes with rabbits. Stupid, helpless, laughably harmless. Rabbits. Got it?
Only, there's something a little weird with the rabbit things. 90% of them are normal critters, doing their rabbit thing, basically being victimized by everything else in the food chain. Some of them, though...they're strange. They appear to have social structures far beyond those of typical prey animals. Rudimentary structures, strangely socialized behavior, high mortality rate (100% in fact, but we don't know that yet). We've only seen them from a great distance. They're not aware of the humans.
Humans being humans, they study the predators first. Duh. Shark week, you know? Fascinating, nasty bastards. Giant teeth, jaws like earthmovers. Scary. There's one that''s obviously old and/or infirm. As soon as its limp becomes noticible (I guess this things have to be somewhat social, like lions), the entire pack turn on it and rip it to utter shreds. They don't eat it (although the humans' first thought is 'cannibalism') , they just destroy it. Obviously, this is learned behavior. The big bastards know what happens when one of them dies, and they aren't taking any chances. To the humans, though, this is strange.
The oldest, and kindest of the humans, is fascinated by the rabbit things. They're dull to the others, so he spends his days watching them...alone. He befriends the rabbit things as he loses his strangeness to them and they lose their fear of him. He reads to them. Tells them stories. Until one day...
The other humans find the old man dead. He's been attacked, but by what, they don't know. This freaks them the hell out, but it gets worse. They prepare him for cremation (no burial on a new world, sorry), do their mourning, and, before they burn him, he stirs, staggers, and stands, saying:
"We need to talk."
Dammit. There's no way the humans aren't going to realize that the rabbit things are dead. The body temperature is going to give that away. Reptilian creatures maybe? Not quite what I wanted, but the lizard vibe could be useful here too. Cold-blooded rabbit things? Why the fur then? No, I'm afraid we're dealing with something that has a skin that doesn't preserve warmth. That'll work. Either that, or the parasite restarts the circulatory system. That means breathing. Well, I guess that makes talking easier, although it's funnier to just croak out whatever air fills the dead, still lungs.
I think this can work. A story to begin with the establishes the rules essentially in a vacuum, away from human society. The parasite obviously has to make its way back to earth. At that point, we have the vampire problem. That being: We need a rationale for these being not taking over the entire world in short order. What's to stop them from taking over the whole deal? The must reproduce very slowly, if at all. Or maybe earth is inhospitable to their reproductive cycle. That limits the total number of these parasites that can exist at once. Sure, they burn through bodies quickly (have to do some math on that one), but if the number is small enough, they're never going to take over. They'll be damned easy to detect, what with the body being dead and rapidly consuming itself, but...if they don't need physical contact to jump, then killing them is a bitch.
I'll think on this, sleep, and then revisit it and make a list of problems that need to be researched or explained.