Bluth himself would later make several changes to the story, most notably with the addition of mystical elements not present in the original novel. He explained "Regarding magic, we really believe that animation calls for some magic, to give it a special 'fantastic' quality." This was most apparent in the magic amulet given to Mrs. Brisby, which was meant to be a visual representation of her character's internal power; something harder to show on film. The object was also meant to introduce a spiritual aspect to the plot, with the director remarking, "The stone or amulet is just a method of letting the audience know that Mrs. Brisby has found 'Courage of the Heart'. Magic? Maybe. Spiritual? Yes." In the same vein, Nicodemus was made into a wizard to "create more mystery" about himself and the rats' colony. The antagonist Jenner was given much more prominence in the movie, being only mentioned as a traitor who leaves in the book, to "add drama" to the narrative by giving it a more visible enemy. Justin also now succeeds Nicodemus as the leader of the rats to give his character more of an arc and allow him an opportunity to "grow and change." Unlike the original work, Justin does not rescue Mrs. Brisby from the cage at the Fitzgibbons' house and she now helps her children without the rats' assistance by using the amulet; once again giving focus to her personal story. As Bluth put it, ""The Secret of NIMH" is really a story about Mrs. Brisby and her need to save her children. If the rats save her children, then she hasn't grown in the film."