Peter nodded and moved over to an empty corner of the room, well out of the way of everyone. He wasn't sure why he felt that he needed the extra space. If it worked, then he'd be tiny, and if it didn't, well, he'd be the same exact size as he was now. Shrugging to himself at his silliness, he took a deep breath and then began to do shoulder rolls to relax whilst he concentrated on his breathing.
Think of how you'll look, he told himself. A tiny, brown rat, with a hairless tail and big brown eyes, and a twitchy nose...
He closed his eyes and clenched his fists, screwing up his concentration, and then he began to feel a little sick as his centre of gravity shifted. Peter's eyes flew open, but it was already too late to stop. The Shack had suddenly began to grow, grow, grow right in front of his eyes. Then next thing he knew, he was looking up at three huge people and getting an all too good smell of an extremely musty rug.
Peter went up on his hind legs, lifted his head, and moved his nose all around, sniffing to get a better sense of his surroundings. He couldn't see too well, but he could smell things in a way he never had before. James was over there, and Sirius was over there, and Remus was over there, and he knew that all just from his nose. He gave an excited squeak scampered across the floor in James' direction.