Gullible's Travels Puns

Context: My little sister (10) was making gullible jokes, e.g. "Did you know gullible isn't in the dictionary?" or "Gullible is written on the ceiling."

I'm pretty sure this should go down in Dad Joke History:

Dad: I read a book growing up, it was called "Gullible's Travels"

Sister: What was it about?

Dad: About 200 pages.