This reminds me many years ago when I found in a toy shop a book about horses. All pages were completely filled with "Cloppete cloppete cloppete" (a funny way to write the italian onomatopoeia of a horse trotting). There was a complete series of books like that. Each had one typo and if you found it, you could send a post card explaining the typo and win the whole series.
I actually found it by chance (a new sentence starting with a small "c") but never bothered to buy it anyway.