The sproinger - wind it up, hide it, bury it, and wait for the suprise! See video here: http://www.youtube.com/watch?v=ynXMh04gT0Q&list=HL1367620895&feature=player_detailpage Requires one sacrificial kitchen timer, as pictured, and one spring (in this example, 1" compressed, 3" expanded). Remove the timer mechanism, and install the printed sproinger parts. If your printer is lame like mine you'll probably need to use a file to adjust the fit a bit...but you oughta be able to get it moving smoothly. Compress the spring halfway so that the "launcher" meshes with the "spinner" and wind the spinner clockwise to set delay. Compress the spring fully and rotate the "launcher" CCW until it bumps the nearer stop, then hide it, place your ammo on top of it, and wait!