The following text is for questions 11 to 15. 

    One day, a farmer found a giant egg and decided to cook and eat it. After eating the egg, he gradually changed into a giant dragon.

    The giant dragon decided to live in a deep river near his village because he realised that he could not live with humans anymore. The dragon lived there peacefully. He also ate fish which he could find easily in the river.

     However, big fish living in the river felt threatened by him because they were afraid someday the dragon would eat them too. So, one of the big fish came to see the dragon and told the dragon that there was another dragon coming to challenge him to fight. The dragon was furious about the challenge, so he agreed to wait for the other dragon coming to fight.

     While he awaited his rival impatiently, he was swimming here and there to calm himself. The water moved fiercely as he moved. The dragon thought that the water movement was because of the other dragon coming. So, when he saw a tail, he bit and pulled the tail fiercely until he bit it off. He, soon, realised that it was his own tail, but that was just too late. The dragon died because of losing too much blood.

"The dragon was furious about the challenge ... " (Paragraph 3)

The underlined word means ....