Brienne's thoughts went to the small box on the desk before her. White mouse! White mouse white mouse white mouse! She concentrated and thought hard at the box. Probably she'd have a stroke by the end of this. Well, not literally, but it damn well felt like it. The small box started to blanch, each inch turning white. Soon, it was as white as fresh snow. Then, fur started sprouting up like little blades of uncolored grass, through the "snow", "covering" itself. Brienne stroked it, it felt soft like down on a newborn and dried chick. The box then grew four legs, each with a fleshy paw on the end. Each paw had slender-ish "fingers" with clear claws at the end. Much like a rodent. Little white ears popped up next, as well as eyes, and a complete snout. However, now the thing had no tail and the general shape of a box, still. That was fixed in a hurry when she concentrated more on what the mouse should look like. The mouse's rear-end rounded out, but included a bump indicating it was of the male gender, and the tail slithered just above the bump. The body rounded out more, narrowed at the neck, then widened a little at the head. Brienne marveled at the little guy. He looked like a real mouse, in fact she deemed him a real mouse. The little white creature crawled up on her hand and onto her shoulder.
She raised her hand, then stated "This is fun, I wish I had another box so I can do this again, but with different colors".