The Toy Bull is a non-sentient object. Donald uses it to pretend to be a ferocious bull while the Caballeros play a bullfighting game. The tip of its tail consists of a large number of dynamites to which when lit, it causes it to explode.
The Toy Bull is one of the objects from Mexico seen when Donald hits the piñata he received for his birthday.
It is later used during the end of the film when the Caballeros are playing a bullfighting game. Things later get chaotic when José Carioca lights fireworks on the tail, sending Donald out of the toy. The force of the fireworks animating the toy, Donald is chased until the bull is punched into the air, providing the fireworks that close the film.