In the posters for Horton Hears a Who!, I never really understood why it looked like Jojo was about to blow into a horn. Years later, I realized it's supposed to represent his defining moment in the movie when he saves the Who world by shouting "Yopp!" into that very horn.
After frantically searching for the clover, Horton is described as being "more dead than alive". When you read the book as a kid, you think nothing of it...but when you happen upon it when you're older, you suddenly think "Oh my god, is he about to diefromexhaustion?!"