Mr. and Mrs. White heard a knocking sound after Mr. White had made his second wish. His second wish was for Herbert to come back alive. They were confused after they heard the noise and thought that they had a visitor.
They slowly went down stairs to see who their visitor is. Then Mrs. White had realized that maybe the visitor was Herbert. She told Mr. White this and Mr. White told her to not open the door because it might not be Herbert.
Mr. White then went upstairs and grabbed the monkey's paw. He thought that if Mrs. White opened the door something bad might happen. So, he made his last wish and it was for Herbert to not come back alive. They did not want anything bad to happen to them again.