One day a lawyer's (律师) wife fell iii and he went to get a doctor. The doctor went to see tile woman, but before he went into the house he stopped. He knew that the lawyer never paid his bill (账单). So he said to the man, 'But if I do cure (治愈) your wife I'm afraid you may not pay me.' 'Sir,' said the lawyer, '' here I have $ 500. Whether you cure my wife or whether you kill her I will give you all this.' The doctor was now sure of the payment and went into the house. When he reached the woman's bedside, it was soon clear to him that he could do little. She was badly iii, and though he gave her some medicine to take, she soon died. He told the lawyer he was very sorry, then asked for the money. 'Did you kill my wife.'?' asked the lawyer. 'Of course not,' said the doctor. 'Well, did you cure my wife?' asked the lawyer. 'I'm afraid that was impossible,' answered the doctor. 'Well then, since you didn't kill her and you didn't cure her, I have nothing to pay you.' Before the doctor went into the lawyer's house he stopped because ______.