Zoroa and Metiph rolled around in the grassy clearing, giggling as they kissed passionately. Distracted as they were, they didn't notice the small animal until it was only a few feet away.
Pulling away from Metiph's embrace, Zoroa exclaimed, "Oh, look! It's a squirrel!"
She reached out her hand, but without warning, the creature leapt forward, biting her on the arm. With a yelp, she jumped up, and the two of them stomped on it until it stopped twitching.
Its body was filled with pieces of metal.
Looking up at Zoroa, Metiph backed away, a look of horror in his eyes. He ran back to the village as fast as he could, and never looked back.. When the hunting party found what was left of Zoroa shambling through the woods several hours later, they beat her with clubs, and buried the remains.
What would a postapocalyptic game be without zombies? Putting my own spin on them, though, the upshot is that before the Apocalypse, scientists were working with nanobots that would augment humanity, replacing diseased or damaged body parts. It worked - sort of. They could teach the nanobots to replicate the form of the body, but not the functions. So a replaced liver would just be a liver shaped piece of metal. The project was considered a failure, but a failure with promise, so the nanobots were put away for future study.
In the years following the End Times, the laboratory where the nanobots were housed suffered structural damage, and the nanobots were released into the wild. Their time in isolation had warped their programming, turning them into an agressive, self replicating virus. For hundreds of years since the Plague, as it has come to be known, has bedeviled the recovering world.
The nanobots are transmitted via fluid exchange, and drive the host to infect others. Slowly, the creature's organs are transmuted into nonfunctional pieces of metal, until the host loses the ability to function, and collapses. Without life functions, the nanobots perish themselves, but while the creature is mobile, it is infectious.
There is no cure, and the infected are put down without mercy. Entire towns have been lost to the Plague, so no chances are taken.