I think "the hat" was a metaphor

Did you know …

That “Dr.” Seuss was not actually a real medical doctor? It’s true!

That is to say, he had been a real medical doctor, but his medical license was revoked after too many failed experiments in which Seuss attempted to place an ape’s brain into the body of a cat. I say “too many” because, initially, Seuss’ research had plenty of supporters; a lot of people were excited to see a real-world approximation of the famous “Cat in the Hat” character.

Unfortunately for Seuss and for the cat and ape populations of his town, attempt after attempt failed, until Seuss made the mistake of using as research subjects his main funder’s pet cat and pet ape. Seuss knew it was a gamble, and it didn’t pay off.

Also, for anyone who feels the need to be a smart-ass, I’m well aware that his real name was “Theodor Geisel.” For your information, however, Geisel absolutely insisted on being called “Dr. Seuss” while he was operating, and during this period he was essentially always operating.