your dog hans loves to ride in the car. whenever anyone picks up a set of keys he races for the door. when your grandmother, who is afraid of dogs, arrives for a visit, hans is not allowed to ride in the car. by the end of her two-week visit, he has ceased going to the door when the keys come out. however, after a brief vacation away from home, he's back at the door again as soon as he hears the keys. why?