It's an age-old feud that started when the Cat King decided to fool the Dog Prince, who had asked for his most beautiful adopted daughter, a mouse's, hand in marriage. Instead, the Cat King delivered unto the Dog Prince a whistle, which the Dog Prince took offense to. Because the Mouse Princess had actually loved the Dog Prince, she was insulted when she learned that the Cat King had decided not to allow her to marry the Dog Prince, and thus she and the Dog Prince conspired to overthrow the Cat King. An informant Raven, however, told the Cat King of their plans to slip poison into his catnip and elope with one another, so the Cat King banished them both from his land, promising that if he ever saw either of them again he would have them promptly put to sleep. Thus dogs and mice are not particularly opposed to one another, but whenever a cat becomes involved there is a great fuss and tussle that usually must be broken up by an exasperated human who just wishes they could get along. The end.

Why do people sing?