A Blueberry is an entity that is significantly larger and heavier than a normal human. While blueberries as fruit are natural, blueberries as an entity can only be achieved by ingesting the Three-Course Dinner Chewing Gum. The only confirmed species are 20 Oompa-Loompas and Violet Beauregarde.
When first going through the transformation, the victim's nose slowly turns blue, and it spreads across their face. The color change then speeds up, affecting the victim's hair and neck before spreading to the rest of their body. When the victim had turned completely blue, the swelling portion starts, starting with the victim's hips and lower body and turning the victim's garments blue. The butt instantly doubles in size as the stomach starts increasing in size, with the inflation speeding up. The whole body then starts swelling, doubling the size of the victim's cheeks and slowly sucking the victim's head, feet, and arms into their body, all the while increasing in size. The transformation stops abruptly, but not before the user reaches an absurd height and becomes completely round, save for sunken indentions at the hands, feet, and head. The victim is left supported unable to move their body and can only be rolled around. In this stage the blueberry is "ripe."
The juice from a blueberry can be removed via juicing. However, the size of the blueberry may be a factor in the juicing's success, as Wonka is unsure whether Violet would return to normal due to her size.
The process of the blueberry cannot be completely reversed even when juiced, as the skin is now a permanent shade of blue. However, juiced blueberries gain access to inhumane flexibility as a result of having a stretched out body.
Twenty Oompa-Loompas have undergone the transformation while testing the gum, however, none of them show up on-screen.
Probably the most famous blueberry is Violet Beauregarde, who stubbornly ignored Willy Wonka's warning and chose to chew the gum, transforming her into a blueberry. Luckily, she was juiced before she became ripe, thus retaining some of her human traits.