Paging Lady Bracknell
When Lady Bracknell has finished reading a book, she sets the bookmark which she has been using to one side.
Regardless of how little time has elapsed between this action and Lady Bracknell taking up a further volume to peruse, the bookmark will not be where she left it. Not only will the bookmark not be where she left it, it will not be anywhere in view. Neither - unlike the majority of objects which go missing on purpose - will it re-emerge once it has been replaced.
Lady Bracknell can clearly recall the appearance of many bookmarks which she has brought into Bracknell Towers over the years, but not one of them has deigned to remain by her side.
Readers will gain some understanding of how desperate the current bookmark-drought is when they learn that Lady Bracknell is reduced to marking the page in the book she is presently reading with a small, dried leaf which Caspar had the great foresight to carry in on her tail.