镇店之宝

　　Mr. Laffler invites Mr. Costain to join him for dinner at a private club that he describes as a very special experience. To his disappointment, Laffler is informed that the house specialty, a lamb dish, is not being served. They continue to visit the club and one evening, the famous dish is served. It also happens that a long-time member has resigned. What, if anything, do the two events have in common?