Entitled "First Editions, Second Thoughts" Sotheby's upcoming auction of first edition books shows revealing handwritten insights into the thoughts of the authors.

The highlight of the sale is a first edition of the first Harry Potter book, "Harry Potter and the Philosopher's Stone" which features comments from J.K.Rowling and drawings.

One of the revelations is where the idea for Quidditch came from.

"Quidditch was invented in a small hotel in Manchester after a row with my then boyfriend. I had been pondering the things that hold society together, cause it to congregate and signify its particular character and knew I needed a sport. It infuriates men…which is quite satisfying given my state of mind when I invented it," Rowling's handwritten notes read.

The personal illustrations include Harry as a sleeping baby on the Dursley's doorstep.

A first edition of Hunter S. Thompson's "Fear and Loathing in Las Vegas" features graphic extra illustrations by Ralph Steadman-Hunter.

While a first edition of Roald Dahl's "Matilda" features the scratchy pen and ink drawings by Quentin Blake.

And in Helen Fielding's "Bridget Jones's Diary" the author questions "I wonder if all this is still as hideous for 30-somethings?" at the end of a paragraph where Bridget is quizzed as to why she is not yet married.

Ann Martel, author of "Life of Pi", personally drew a squiggle with a small boat moving along each page, so that when the pages are flipped it looks like the boat is moving.

The Sotheby's auction of 50 contemporary first editions is on Tuesday, May 21.

No estimates have been given for the books because it is a charity sale and Sotheby's did not want to suggest that one author is more important than any other.

The proceeds will go to English PEN, which is the founding centre of a worldwide writers' association which defends the rights of authors and readers.

Presented by Adam Justice