Dean figured something was going one. But understood in a way what was going on between the man and the girl. They were close, but Dean couldn't place in what way? What threw Dean off was that the man knew what they were. Did they know they were hunters? That meant they must be too. Placing a hand on Sam's shoulder, letting his brother know to let it go. Dean had a plan going within his mind anyways that involved keeping tabs on the two. "Come on Sam. We'll just keep an eye on them for now while we do our own investigating." He wanted to keep an eye on the girl.