When a rabbit begins saying "moo," it helps the other farm animals realize that they are not limited to their own language, and one by one they begin to join the others in making the noises they like best.
When the wind blows so hard that it blows the quack right out of the duck, the oink out of the pig and so on, Bonnie Bumble works hard to get each animal's sound back where it belongs.
When Farmer Brown goes on vacation, leaving his brother Bob in charge, Duck makes trouble by changing all his instructions to notes the animals like much better.
