Kruder, from The Pathfinder's school, teaches you how to make a spring spear trap with almost all natural materials. This is a very dangerous trap so be warned and be very careful if you practice this. By using any springy tree (he uses a Maple), and a toggle tied to another tree, you can make a trip wire for any sized animal. Add a spear to make it more effective. You'll learn everything from the materials to construction in this video.