I’ve been innovating on bookmarks for decades. Money, receipts, paint swatches, entire spiral notebooks, ripped off corners of magazines… bookmarks are everywhere!

Basically anything that will fit between pages and is in reach is a bookmark.

Silliest thing I ever used as a bookmark was a refridgerator. It did require taking the book to the bookmark though.

Including the cover of another book.

Perhaps a book that keeps track of the reading progress automatically. /s

Yes! A method to easily understand completion status without having to open a book to verify progress.