John flips back to Mona's index page and reads an insanely long reference guide on San Lorenzo's local Betty Boop.
He shows the index to the Mintons, and Claire Minton says she thinks it's self-indulgent for an author to index his own work.
Oh, yeah, Claire used to be a professional indexer, and apparently, that's a real job. Huh, the more you know, right?
But it gets better. Thanks to her trained eye, Claire can read Philip Castle's character by how he indexed the book.
She can tell the following about Philip: he loves Mona, has issues with his father, is insecure, and will never marry her.
John asks why not, but Claire says she won't say. Her final words of wisdom are "[n]ever index your own book" (55.23). Words John—or Vonnegut—must have lived by because Cat's Cradle doesn't even have an index. Oh wait, it's a novel.
Later, Mr. Minton catches John on the plane and tells him the reason Philip will never marry Mona is that he's a homosexual.
Claire is so good she can tell that from just the index.