“Belinda tickled him, she tickled him unmerciful…” Why?
Belinda tickled Custard unmercifully to mock his cowardice. While Belinda and her pets boasted about being brave, Custard was a realio, trulio, cowardly dragon who always cried for a nice safe cage.
To tease his timid nature, Belinda giggled till she shook the house and tickled him without mercy. The other pets also joined in the mockery, rudely calling him Percival and asking his age. They all sat laughing in the little red wagon, finding great amusement in Custard's fearfulness.
Explanation
Belinda and her pets constantly made fun of Custard because he was afraid of everything and wanted a safe cage, unlike the others who boasted of their bravery. The tickling was a part of this mockery, highlighting the contrast between their false bravado and Custard's honest fearfulness.