In "The Monkeys Paw," why do Mr. and Mrs. White believe that the second wish has not come true?

In W. W. Jacobs's short story "The Monkey's Paw," the White family, mother, father and son, come to be in possession of a supposedly magical monkey's paw. According to Sergeant Major Morris, the paw will grant its owner three wishes. In an ominous explanation of the paw's power, Morris explains that one of the paw's owners asked for death with his last wish. Nevertheless, Mr. White obtains the paw and uses his first wish to ask for enough money to pay off the mortgage on his house. The very next day he is promptly rewarded with just that amount when his son turns up dead in an accident at work. His wife, overcome with sorrow, pleads with Mr. White to use the second wish to bring the son back to life again. In the immediate aftermath of making the wish, nothing seems to happen, and the couple goes to bed thinking the wish has not been granted. They seem to forget that the first wish did not happen immediately. They also do not take into account the fact that the cemetery where the son was buried is two miles away. Moreover, the son was badly mutilated in the incident and is now a hideous corpse who is most certainly slow and unwieldy. Soon enough, however, Mr. White is awakened by a sound, and then a loud knock brings Mrs. White from her bed as well. She says,

"It's my boy; it's Herbert!" she cried, struggling mechanically. "I forgot it was two miles away. What are you holding me for? Let go. I must open the door."

Realizing that his son is now a terrible monster, Mr. White finds the monkey's paw and, with his last wish, summons the corpse away just as Mrs. White is about to open the door to let the thing in.