A book cries every time it's page corner is turned down.
I'm certain of it. Every book that isn't read in one sitting should have a bookmark (and only a bookmark) mark the spot. Turning the corner of the page down should never happen.
I always use bookmarks - I have a huge collection. But failing the easy access to a bookmark I use a scrap of paper, a thread or anything else I can find lying around.
What do you think?