An Introduction to the Theory of Groups

Unless you studied university-level algebra, you probably never encountered this book. And even if you did, you probably never bothered to really read the index. If you do, check out the entry for Moishe Pippik. It reads:

Pippik, Moishe     (see Navel, Morris)

Which automatically leads the reader on the following trail:

Navel, Morris     (see Ombellico, Mario)
Ombellico, Mario     (see Nombril, Maurice)
Nombril, Maurice     (see Pippik, Moishe)

Which forms, as any reader of the book could tell you, a perfect cyclic group. The words Pippik, Navel, Ombellico and Nombril all mean “bellybutton”, BTW.

And in a totally different note: Most non-Hebrew speaking readers will find a very strange thing in the first page of this book: the dedication is printed in Hebrew. This isn't an in-joke. The dedication roughly translates to: “In the eternal memory of my father and respected teacher, Eliyahu, son of Yosef Yona HaLevi”.