Why is the narrator in Billy Marginalia so tickled?

There is no narrator in Billy Marginalia. Billy Marginalia is a character in the novel The Amazing Adventures of Kavalier & Clay by Michael Chabon.

While Billy is often depicted as a quirky and humorous character, there's no specific instance in the book where he is described as being "tickled." It's possible you're thinking of another character or another book entirely.

Could you please provide more context or details about what you're referring to?