In Matilda What did the Trunchbull do to boy who spell word what?

In Roald Dahl's "Matilda," the Trunchbull, the terrifying headmistress of Crunchem Hall, punished a boy named Bruce Bogtrotter for spelling the word "hippopotamus" correctly.

She forced him to eat a giant chocolate cake, which was much larger than he could possibly eat, as a form of humiliation and punishment.