"well mr terror,what do you think you can do to me ?what is the importance of these words.

When Douglas was in the middle of the lake, he put his face under water and saw nothing but bottomless water. The old sensation returned in a miniature. Then he had to say "Well, Mr. Terror, what do you think you can do to me? ". This time, William laughed at the terror and said to it that it could not harm him. He saw that the fear was vanished and he resumed his swimming.