I was distinctly amused to open the second book, Death at Gallows Green, and find a bright pink post-it with a "necessary spoiler":
Okay, thanks! When the girl finally turned up missing, I remembered that she was not going to be hurt or killed and that therefore, she had to be found. And she was!
More amusingly, to me anyway, was finding the word "pitcher" scratched out on page 55, and replaced with "jug".
On page 56, "pitcher" was unassaulted.
And on page 58, it was again struck out!
The great mystery is why a jug and not a pitcher. Why? British vs. American usage. The book - though set in England - was written by a pair of Americans.
My favorite part? Adding my own annotations to those the book came to me with.
Do you write in your books?