Most bookmarks are made of strips of paper. This one is quite different. The inventor wanted something completely different for his books after reading. So he made this wooden triangle shaped object. It comes in three kinds of wood: birch, beech and oak
I think your book will fall open on the position you have placed it on this Bookhook. I have not tried it, but I suspect it will alter the spine of your books. If you have experience with it, let me know what you think of it.
Thanks to Geegal for submitting this gadget.