The first thing that happened was that Carl rapidly shrank, losing at least two feet in height even as he retained his proportions. Adam was surprised at how quickly that had happened, since the changes were supposed to take a full minute.
"Whoa." Carl squeaked, putting his hands out on the carpet in front of him to catch his balance from the quick change in stature. "That was, strange. I... I feel sort of warm and tingly all over. But why am I so small? Are you just shrinking me to doll-size or something? Maybe I could ride one of your dinos around the room!" He laughed, a feeling of happiness spreading through him as the changes progressed.
His clothing suddenly seemed to blur, fading to a patterned gray, white and black as it seemed to sink into Carl's body while puffing up at the same time, the fabric breaking down into individual threads that fluffed out as it spread to cover his hands and bare feet. "What's this?" Carl chuckled, "like a furry set of footie-pajamas? Ohh, it feels so warm and soft all over, bro, this is awesome!" Something felt like it was tickling the base of his spine, and Carl gave a groan of pleasure, like when you have a good stretch, but he couldn't see the long-furred tail that pushed out above his buttocks because he'd closed his eyes at the sensations assaulting him.
Adam could see though. And he no longer felt guilty as he watched his brother enjoying the pleasurable changes altering his body. He'd known deep down that his sibling wouldn't mind being turned into a cute puppy dog - who would?!
Everything sped up as the minute neared it's end: Carl had leaned further forward onto his hands, which Adam could see had shifted into canine paws under the clothing-turned-fur. As his hips lifted from the ground with the stretch, his thighs thinned and shortened, his feet elongating as pads grew under his toes and followed the same path as his hands. Adam's eyes traced the line of his brother's back and saw that Carl's neck was stretching out slightly, a thick ruff of fur growing like a mantle around it even as his long hair seemed to lighten and melt into the coarser coat that covered his head like a fluffy, fitted hood.
Carl opened his mouth to pant, letting an elongated tongue roll out to regulate his body temperature under his new fur. Another growl of satisfaction escaped his throat as his nose and mouth pushed out into a dog's muzzle, the fur racing to cover it and up over his forehead, meeting ears that had pointed and shifted upward as the changes finished.
Adam was in awe: where his brother had sat one minute prior was now a young husky-type dog, panting happily as it lowered its hips to sit on the carpet, looking at him with the same intelligent blue eyes of his 10-year-old sister.
"Adam?" he jerked, hearing his mum calling up from below. "Can you take Carl out and feed him his dinner? Then I'd like you to set the outside table for dinner - your Da's made burgers!"