The word ‘disbelief’ means

Directions: Read the following passage and answer the question that follows.

Once, a mother duck and her ducklings were on their way to a lake. Suddenly, the mother duck saw a fox approaching. She shouted to her children to start running towards the lake. The ducklings obeyed. Then, the duck began walking up and down dragging one wing of hers on the ground.
When the fox saw this, he got happy that the duck could not fly and ran towards her. The mother duck ran, leading fox away from the lake. When she looked back and saw her ducklings already into the lake and knew that the fox now could not reach them, she stood and took a deep breath.
The fox, thinking she is tired, also slowed down, however to his disbelief, the duck spread her wings and soared high in the air.