Fold two pieces of the white letter paper in half. Use a ruler to measure along the fold to find the center of the sheet and place a dot there. Then using the dot as a guide, draw a 2 inch horizontal line from the dot on the fold to the center of the paper
Use scissors to cut the 2-inch line. Fold the two sides back to form triangles. Smooth the folds down. Unfold the main piece of paper and you will find a mouth-like incision. You use your fingers to press the triangles inward so that the "mouth" opens outwards.
Draw around the mouth to create an animal or creature with the mouth for a pop-up. The design of the mouth allows for boys to be creative in the choice of critter that is yawning, roaring or about to eat something.
Change the shape of the line to change the shape of the mouth or make it into something else. A jagged line for example gives the illusion of teeth. Colored paper as a background under the mouth opening can create a tongue or creature inside the mouth (for example a dragon with a gem in its mouth).
Use the heavy construction paper to make a cover for the book. Be sure to glue the pop-up pages so that they can still open, but are secure inside the book.