Harold & Hog Pretend For Real!-Elephant & Piggie Like Reading!

Harold and Hog pretend with the roles they were born to play . . . but which roles are they?
Hog is careful. Harold is not.
Harold cannot help smiling. Hog can.
Hog worries so that Harold does not have to.
Harold and Hog are best friends. But can Harold and Hog's friendship survive a game of pretending to be Elephant & Piggie?