I don't know the story of Oz that well... This illustration makes me curious to know: Which part (and what does it mean) this brain is from?
I'm not sure. There wasn't any explanation on the postcard.I guess it relates to the first book. Dorothy is going to Oz because she wish to come back home, and the Wizard is the only one who can help her. Some friends join her in the way: the Scarecrow wants to get a brain, Tin Woodman wants a heart, and the Cowardly Lion wants courage.In this first books (as well as in the following ones, now and then) "having a brain" or "is better having a heart or a brain", etc. are conversation subjects.
Let me know your thoughts. All your comments are very welcome!