I'm busy collecting 501 new items for a sequel to my Things That Nobody Knows book. These have to be questions that absolutely nobody knows the answers to.
Here are some of my favourites so far:

How did avocados survive the extinction of the giant sloth?
Why do we have five fingers?
Do guinea pigs have innate personalities?
Why do females have orgasms?
Was the Old Testament wrong about camels?

I'm up to 365 unanswered questions so far, so have only another 136 to go, then I can start writing the book.