Following the events of The attack on Modesto, California by mutant pumpkins B.O.B., The Missing Link and Dr. Cockroach discover the first Zombie Carrot in the Murphy's yard created by the remains of the Mutant Pumpkins. They also discover that the Carrot can infect people with a zombie-esque mind control virus by biting them (when Carl Murphy is bitten) and that they multiply when destroyed.
Dr. Cockroach and B.O.B. are forced to retreat into the Murphy house when The Missing Link is infected only to discover that one of the Carrots sneaked in with them. When the carrot bites B.O.B. but he is not infected Dr. Cockroach realizes that he's immune since he doesn't have a brain. To this end Dr. Cockroach states that the only way to defeat the carrots and free their loved ones is for B.O.B. to eat all of the carrots.
Albeit reluctantly B.O.B. tears through the house and eats the carrots until the point that he's morbidly obese and immobile, leaving only one left that he cannot reach. B.O.B. subsequently develops the will power to reach out and eat the carrot when he sees him opening the last Nutter Buddy Butter Bar freeing all of the carrots victims. In the final scene of the short B.O.B., who has been narrating the story, transforms into a giant Zombie Carrot.