Why did Mrs. White go scurrying to the door at the postman's knock?

Mrs. White believed their wish had come true, and that the postman was bringing their $200.00.

"Well, don't break into the money before I come back," said Herbert as he rose from the table. "I'm afraid it'll turn you into a mean, avaricious man, and we shall have to disown you."

His mother laughed, and following him to the door, watched him down the road; and returning to the breakfast table, was very happy at the expense of her husband's credulity. All of which did not prevent her from scurrying to the door at the postman's knock, nor prevent her from referring somewhat shortly to retired sergeant-majors of bibulous habits when she found that the post brought a tailor's bill.