What do you think changed the attitude of the other animals and that of Belinda towards the dragon?

The dragon, Custard, initially commanded no amount of respect from Belinda and the other pets, on account of its cowardice. But when the house was attacked by an armed pirate, the dragon savagely attacked the pirate and ate it up, while all others panicked and ran for shelter. Thus, the other animals realised its worth and came to respect it genuinely.