Silver

Silver and Gold were twins. They spent their entire early life with their hands firmly clasped through the stiff,  unyielding stability of an axle. Not that they were sentient then, but  still they remembered. They rattled along together at the front of a  two-wheeled cart until one day, the cart's handle broke and they found  themselves in the Waste Management Sector. They were sitting in a loose  pile of other rubbish, waiting to be either incinerated or recycled,  when an inventive young Grundo happened along. It wasn't all as  coincidental as you might believe. This Grundo was an aspiring engineer,  and he often rummaged around the edges of the uncompacted rubbish piles  to see if he could salvage anything to practice on. When he spied the  abandoned cart, he almost gave an audible whoop of delight. The handle  might be broken, but there was nothing wrong with the wheels or even the  body of the cart itself. A million possibilities spun through his head  as he pushed the cart back to his workshop. 

The gleaming wheels of his salvaged cart practically twinkled under  the workshop lights. They were like jewels. Or like the sparkling,  excited eyes of his little sister whenever he made a new toy for her. He  suddenly straightened with inspiration. He would make these wheels,  which seemed to already have so much life and personality, into some  kind of robotic Petpet for his sister! It would be perfect for the  energetic, yet slightly irresponsible young Grundo who could probably be  depended upon to forget to feed a real Petpet. After some thought, he  decided to use only one wheel to make the robot. If he made an  irreparable mistake, he would be able to use the second wheel to try  again. Carefully, he removed the wheels from the axle that was holding  them fast.

Nearly a fortnight later, the Grundo sat back in his chair. The first  robot had gone off without a hitch. He had even employed the help of a  friend who specialized in AI to look over his rudimentary personality  programming. With success under his belt, his eyes had fallen on the  unused wheel. Wouldn't it be cute to have matching Petpets with his  sister? It had been such fun making the first one, he decided instantly  to use the second wheel to make a Petpet for himself. His friend helped  him tweak the AI a bit so that the two Petpets would be distinct and  unique from each other. To keep them straight, he spray-painted one with  gold paint while for the second he simply buffed the metallic surface  into a shining silver.

On the Day of Giving, the Grundo unveiled his surprise to his little  sister. With great suspense he activated their circuits, and the two of  them held their breath as the lights in the Petpets' eyes slowly blinked  on. With a whirr the silver one slowly rotated its little body for a  few revolutions before moving over to nudge the gold one. The little  gold one looked around, until its gaze landed on the smaller Grundo,  whose eyes were as wide as Kreludor. Clicking and beeping sweetly, it  made its way over and bumped the little girl gently on the knee. The  Grundo giggled and sweeped the Petpet up in her arms before running over  to hug her brother.

ʺI'm going to name her Gold, because she's gold.ʺ
ʺI suppose I'm to name mine Silver then.ʺ
ʺWhat do you call them, Bubby?ʺ (This was what she called her brother,  ever since she was a baby and still couldn't pronounce the word  "brother" completely.)
ʺI called them Rotawheels in my notes while I was building them.ʺ
ʺGold the Rotawheel,ʺ she sighed happily.
ʺSilver and Gold,ʺ he nodded in agreement.