From Classic Puzzles for the Classroom:
The invertible, a picture that depicts one thing when held right side up and another when held upside down, was one of the most popular features of the comics puzzle page. From a puzzle standpoint it is an odd beast, being perhaps closer to an optical illusion than a true puzzle for the reader (though arguably not for the creator).
Might become a giant Roc in panel 8.
Here is another sample of Verbeek’s work followed by some of the invertibles you would have seen in Golden Age comics.