We rescued a stray from a shelter and named him Sully. We've had him for almost 4 full days days and he doesn't seem to understand his name. Maybe he is just stubborn, but I don't think so. He doesn't look at us when we say it. Our last dog was a shelter dog and understood it by the 3rd day. Another name we were going to call him was Cooper. I'm not sure if we should change it.