Briefly: Hidden Mickeys are all the rage when it comes to classic Disney stuff. You can find 'em in the parks, the movies, and almost anything else. What isn't common, however, is a hidden Oswald.
That's right, Oswald the Lucky Rabbit, Walt's creation before good ol' Mickey, makes a guest (and almost invisible) appearance in the Up Little Golden Book! (See the close-up above and full page below, thanks to CB).
I love seeing a 'revival' of Oswald, one of my favorite early Disney characters, especially in something Pixar-related! This just shows how comfortable Disney and Pixar are getting together. Isn't it nice seeing them get along so well after all of the previous conflict?
Source: Cartoon Brew