Dr. Sheeler was surprised at Mr. Nelson’s call because

A physician can expect to be called at arty hour of the day or night, wherever he is, whatever he is doing. It’s just part of the job.
     Dr. Sheeler was no exception. He, however, had received no calls from the Nelson family in quite some time and was a bit surprised when one night, shortly after he had fallen asleep, the phone rang and he heard, "Doctor, this is Jim Nelson. Come right away. My wife is in pain. At first it was not serious, but now the pain is very severe. She just sits here groaning and clutching her side. I’m sure it’s appendicitis."
     Recalling what he remembered about the Nelsons, Dr. Sheeler tried to calm the near-hysterical man at the other end of the line. "Now, now, Mr. Nelson, it can’t be all that bad, probably just ind  igestion. I’ll come around the first thing in the morning."
   "But, doctor, I’m sure it’s her appendix. You’ve got to come now. My wife’s life may be in danger!"
     "That’s absurd," the doctor said disapprovingly, now somewhat irritated at the other man’s insistence. "I took your wife’s appendix out two years ago. You know as well as I do that she hasn’t got another one."
     "I know that, Dr. Sheeler," said the sad husband. "But last year I got another wife."