Sans could tell something was off when chara just kind of walked away from him. He walked over to her and sat down on the other side of her, so she was in between him and Frisk "heh heh... yeah... that house could have some cool old treasure in it or something" Sans turned to Chara, he wasn't being serious. He just wanted her to talk about it, even if he didn't address if she was feeling weird the way she would talk about it would obviously make him realize something would be off. "maybe we should head inside of it.. try to find something cool?.. or we could just explore around it heh heh.. what do you guys think?"