Frog wakes up one morning feeling sad, but he is not sure why. His animal friends are worried about him and try to cheer him up: Little Bear reasons that he was able to be happy yesterday and Rat does some crazy dancing and acrobatics, but Frog didn’t even smile. When Rat plays a beautiful tune on his violin, Frog begins to cry. Frog explains that he is crying because Rat is playing so beautifully. Rat thinks this is silly and bursts out laughing. Suddenly, Frog begins to smile, and eventually he laughs and sings with Rat and his sadness has gone. His other animal friends here the commotion and come running, and they all laugh together. The book concludes with Frog announcing that he has never laughed so much in his whole life, ever!