Neville ate his own portion as the dog did, though slightly less enthusiastically. He watched though, with a little bit of a chuckle, and couldn't shake the feeling that he was missing something. Like there was this thought somewhere in his mind just out of reach.
It wasn't until the food and water were both gone and he was reaching out to answer the almost-handshake that it came to him. Something about the way the dog's eyes looked just made the thought click. "Sirius Black?" he asked, tone hushed but letting slip the name before his thoughts had time to catch up with his mouth. Obviously, if he were staying as a dog there had to be a reason for that and here Neville was, just blurting it out.
Though he wasn't sure if that were better or worse than if he were wrong and he was just talking to an actual dog thinking it was a person.