This UPA animation done by John Hubley is one of the greatest examples of how important sound design is to an animation. Matter fact, this very piece is all about a boy, Gerald, who cannot speak except for his abilities to make great sound designs as a way of expressing himself.
I am running a summer camp of sort to entertain my daughter and her friends for two hours a day so they have something to look forward to that's engaging and I showed at least one great animation everyday. I was pleasantly surprised that this is overall favorite of theirs. It just shows you great animation with a good story and execution never go out of style.