Why were the Oompa-Loompas rolling a big blueberry in Charlie and the Chocolate Factory?

In Charlie and the Chocolate Factory, one of the five children who had a golden ticket that entitled her to a tour of Mr. Wonka's factory was Violet Beauregarde. Violet's obnoxious habit was chewing gum. When Mr. Wonka led the children and their parents to a room where he was working on an amazing new type of chewing gum, Violet reached out her hand, snatched one of the experimental sticks, and popped it into her mouth—despite Mr. Wonka's warnings that she shouldn't. As she began chewing, the gum produced all the flavors of a full meal. But when she reached the dessert course, blueberry ice cream, Violet began to turn blue. Soon she began to swell up like a balloon. Mr. Wonka clarified: "Like a blueberry."
Soon she was nothing more than a huge swollen blueberry with skinny legs sticking out. The Oompa-Loompas appeared and began rolling her down the corridor. Charlie asked whether the girl would always be a blueberry. Mr. Wonka explained that the Oompa-Loompas would take her to the de-juicing room, where she would quickly be squeezed until she was "thin as a whistle." So the big blueberry the Oompa-Loompas were rolling was Violet, who had become a blueberry by pursuing her obnoxious chewing gum habit despite Mr. Wonka's orders. She was being rolled to the de-juicing room in order to be restored back to "normal."