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.
Despite Jojo being claimed to be the smallest of his kind, one of his sisters is smaller than him. It can be explained that she's still a baby and once she grows up, she'll be taller than him.
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?!"