and as you can see, it's pretty rigid. this inmate lodged a metal screw for the tip. when the officer or inmate walks by the cell, the spear is thrust out. >> you wouldn't think that a rolled up newspaper or magazine would be -- make that good of a handle and it does. very effective. >> this is known as a zip gun. this portion of the zip gun is filled with match heads, ground-up match heads. a plunger is used to push shrapnel, pieces of metal, ground up zippers, packs it down. when his target walks by, the inmate would light those two fuses. basically what you have is a double-barreled shotgun. >> what's particularly scary is once an inmate finishes making his weapon, he finds a clever place to hide it for quick access. >> it's an old joint.