Students will probably see the angle-fold move up toward the gutter when the book opens, but may have difficulty seeing the back-and-forth motion. The diagrams below show how the angle-fold and its flag move as the book opens. You can see the flag traveling along a path that goes both upwards and to the left.
You can’t see inside the book when it’s closed, so it might be hard to believe that the angle-fold hides in the position shown in the diagram at the left. To see the hiding place of the angle-fold and its flag, why not use the see-thru book? In the video below, the location of the angle-fold and flag are revealed using the see-thru book.