Balisong--or butterfly knives--are beautiful to watch, because a well-practiced user can draw, wield and sheath one with a few quick flicks of the wrist. While Balisongs knives can be extremely dangerous, an aficionado can easily make a paper Balisong knife that's safe and cheap.
Fold one sheet of paper in half. Hold it as though reading it, and fold the bottom edge to the top.
Glue the sheet of paper to itself. Open it slightly and spread glue on an inside half, then press the paper together. Wait a minute or two to dry.
Fold the sheet of paper in half again, along the long edge. With the folded edge facing you, fold the left side to the right edge. Glue the page together again as described in Step 2 and wait a few minutes.
Fold and glue the page a third time. Fold the newly folded left edge to the right side and glue as described above. Wait for a few minutes to dry again.
Fold the paper in half one last time, but don't glue it. The paper should now be a narrow strip, so fold the long edge to the opposite long edge.
Fold the long edges of the paper in to the crease. When done, you should have a sort of C-shape in the paper.
Cut along the center crease.
Leave the pieces to dry for about 10 minutes.
Repeat Steps 1 through 4 described above with the other sheet of paper.
Allow the piece of paper to dry for 10 minutes or so.
Place the quarter about 1/4- to 1/2 inch above the bottom edge of the paper, centered. Trace the bottom half of the quarter with the marker, then remove the coin. Draw two tabs sticking out from either side of the semi-circular mark, about 3/4 inches wide and about 1/4 inch in from the edges of the paper. This mark becomes the base of the blade.
Draw a knife blade onto the piece of paper, stemming from the base. You can make it as simple or ornate as you choose, and you can use a real knife as a reference.
Cut the blade out.
Trim the handle to accommodate the blade. Take a handle piece, folded into a V-shape, and cut a diagonal notch into the creased edge, starting about 3/4 inches from the top. The notch doesn't need to be wider than a 1/2 inch cut.
Slide the blade into the handle piece so the tab sticks out of the notch and half of the blade is covered by the creased handle. This is the closed position for the knife; test that it will slip 180 degrees around to the open position.
Punch a pin through the tip of the notched end of the handle, knife tab and the other side of the handle. Turn and wiggle the pin a few times to ream this hole out a little.
Push an eraser onto the exposed pin. Make sure the eraser isn't too tight on the pin, otherwise the hinge won't turn smoothly.
Repeat Steps 1 through 4 with the other handle piece, pin and eraser.
You can also make the knife out of cardboard. You don't need to fold the cardboard, as you do with the paper.