Night of the Living Carrots

Night of the Living Carrots is a 2011 Halloween short animated film, based on Monsters vs. Aliens and produced by DreamWorks Animation. Following the 2009 short, Monsters vs. Aliens Mutant Pumpkins from Outer Space, a mutated carrot has spawned hundreds of zombie carrots taking control of the subjects mind. Dr. Cockroach determines that the only way to defeat them and free their victims is for B.O.B. to eat all of the carrots.

In a theater, B.O.B. introduces the story in a manner parodying that of typical horror films, beginning with a recap of the events of Mutant Pumpkins from Outer Space, and tells the audience to be prepared for a story guaranteed to give them nightmares.The scene then shifts to the twist ending of the previous special. The Zombie Carrot emerges and charges at the camera but is stopped short by a gate slamming into it. Carl Murphy announces to the children of the Modesto suburbs that a costume contest was about to start and that the winner got their weight in candy. B.O.B., dressed as a pirate, takes interest and comes inside but takes all the candy meant for the contest. Outside, he hears a strange voice and is initially frightened by the zombie carrot, but he mistakes it for a child in a costume saying that he thought the zombie carrot was a real carrot. Believing the carrot would win the costume contest, he throws it inside where it immediately bites Carl, turning him into a zombie. ........

Source: Wikipedia