As neither she nor her husband smoked, Mrs. Richards was surprised to see cigarette ash on her doorstep as she entered the house. When she opened the living-room door, an unusual sight met her eyes. A strange man had taken advantage of her absence and was fast asleep in an armchair! Taking care not to disturb him, Mrs. Richards left the house immediately. She called a taxi and went straight to the police station. When she got there, she hastily explained what had happened and added that the man must have got into the house through an open window. Mrs. Richards returmed home in a police car together with two policemen. But it was too late: the man had disappeared. Hurrying upstairs, she went to her dressing-table. She smiled with relief when she saw that the only thing the man had taken was an imitation diamond necklace which was almost worthless. Mrs. Richards got a surprise because ______.