The door to her office (if you can find it) can be opened. Fans must then pass several challenges to get their treat.

If you don't want to know what the treat is, stop reading now. It's another clue about her next book, Harry Potter and the Half-Blood Prince.

Those who complete the challenges are rewarded with the names of three chapters from the next book.

Peeves the mischievous ghost is in on the act and the challenges also involve selecting a special key and doing some serious snooping around.

Follow-up

Half-Blood Prince is the follow-up to Order Of The Phoenix, published in June 2003, and will be the sixth book in the Harry Potter series.