What surprised him most was not finding someone else in the kitchen or even another dog, but it was the way he spoke to him. It was one thing when the Marauders talked to Padfoot like any other person, they knew the truth, like Lily too - but this man wasn't looking at Padfoot and seeing a man in the shape of a dog, but a dog who he spoke to like a man. It made him tilt his head a little considering them both as he sat there while Winston sniffed around him.
He wagged his tail a little as Will went on, sure he hadn't exactly come looking for a meal or anything like that but he wouldn't mind getting to know these two a little bit more. What was the worst that could happen? He outed himself as an animagus? Maybe he'd startle Will a little with the revelation, but there were worse things.
He padded a little closer towards where Will was working his head tipped up to get a whiff of what he was cutting up and gave a low huff of a bark, making his interest clear.