Dan really wasn't sure about this part. Sure, living the life of a smarter-than-average pet sounded pretty good to his couch potato personality, but actually being part animal? That sounded kind of creepy, like something out of a horror movie. He definitely hoped it wasn't going to hurt, and he crossed his fingers that it wouldn't be too embarrassing.
He listened anxiously as Kat finished her chanting. He was still standing there anxiously waiting for something to happen, when he noticed something out-of-place. There was a loose, bendy feeling in his lower back, and he realized that not only was something hanging off of him back there, but he could swing it back and forth. Glancing over his shoulder, there was a long, yellow-furred, labrador-like tail sticking out.
"Whoa, is that mine?" he asked rhetorically, circling around for a closer look even as he was still waving it experimentally. He managed to catch it with both hands, jumped at the unfamiliar feeling of grabbing himself back there, and then leaned in tight for a closer look. Kat giggled, watching her brother distract himself with a part that didn't belong on a human like that. "Yep, it's all yours, boy," she answered, already calling him by a doggy-like nickname. He ignored her and focused on his tail for a while longer before looking back up at them.
"You... you gave me a tail." He didn't know whether to sound angry, confused, or just surprised.
"Well, yes, honey," said his mother. "You can't be a proper pet without some proper pet parts."
Dan wasn't so sure he wanted a tail, but he was going to have to get used to it, and he was too curious to resist giving it a thorough examination right where he stood. He went back to staring at it, handling it in various ways, twisting it in different directions, looking at it from different angles, and marveling at its coarse but lightly fluffy fur. After a minute or two, he noticed that the sounds around him seemed to be getting louder and crisper. He glanced up again from his new canine appendage, cocked his head, and looked around.
"What's all that noise? ... Oh ..."
Dan felt some new stronger muscles in the sides of his head jerk and lift up the two thin flaps of skin hanging over his cheeks. He was hearing not only the sounds in the house, but also the pitter-patter of animal footsteps outside, the wind through the trees, car engine noises, and some of the neighbors' voices. He couldn't see his new dog ears, but Kat grinned at the sight of her her brother's floppy yellow triangles perking and twitching over either side of his face.
"Am I really going to be a dog, Mom?" asked Dan with some real concern in his voice.
"Not entirely, sweetie, just enough to properly experience the lifestyle."
He felt a moistness in his nose, and he started to detect seemingly stronger smells the more his face stretched out in front of him. By the time whiskers were sprouting out of the sides, he was too fidgety to stay in one place, say anything, or fidget with his new tail and ears. He had to get a closer whiff of these things he wasn't used to smelling. He was pacing all around the room (with his tail standing stiff in a curious expression) sniffing things: the floor, the lamps, the couch cushions--oh, the couch cushions! He could of focus in on all sorts of unique scents where people had been sitting there.
"What is it, boy?!" Kat said in her most mocking pet-talk tone of voice which made Dan stop in his tracks. He stood up straight, lowered his head, and drooped his ears and tail. He hadn't even noticed that short yellow fur had covered most of his body, because he was so fixated on smelling everything like a dog does.
Their mother spoke again. "It's okay, Dan. It's all perfectly normal for your new role around the house. I think it suits you much better. Now I want you both to be good while I go to the kitchen and start dinner."
Dan was an anthro dog now, in a family of witches. For better or for worse, he had everything he needed to live his new life as the family pet. It was going to take some time to get used to this.