The Bear That Wasn't was the last theatrical short produced by MGM. Originally a children's storybook written by Looney Tunes director Frank Tashlin in 1946, the 1967 cartoon was directed by Chuck Jones. Although a story ostensibly for children, it's also noted for its satirical view of corporate culture and mass indoctrination–if something is repeated enough, even if it isn't true, it will become the truth for many.
Here are a production cel and timed drawing from the film:
And the cartoon: