Here's the idea:
You've got a bunch of rusty iron, serrated hooks with random spikes protruding out in every direction. They are hung by piano wire (or cat-intestine-wire, take your pick) from the ceilings of a somewhat dark area. The key is that the hooks will be just below eye level for the average person.
A thief or a warband will pass through the tunnel and through their recklessness, hooks will savagely get caught right between their eye and the upper chin. They will then panic, wildly attempt to remove the hook, and in doing so, tug on the wire that the hook is attached to. This will signal similar hooks, lying on the floor or on the walls, to come flying out, lashing at the victim and if not brutally ripping flesh from bone, get more hooks caught onto the poor sap.
Each time the victim struggles and tugs on the wire, the hooks continue to lash and strike, tearing meat and slowly taking apart the victim with each lash and hook. Hooks that were embedded in the sap pull back with force with each lash, taking with it whatever it was holding onto, be it flesh, eyes, or an entire limb. This process of whipping, hooking, and tearing continues until the victim either dies or stops moving.
Here's where the fun begins. Presumably, if the person had any comrades, this will be the time when they try to save the poor, crying, sniveling, blood-sodden mess of a creature. He will be whimpering to them, about how if he doesn't move, nothing happens, and they've got to save him now. They will cautiously approach the creature who is probably now hanging suspended from the air by a myriad of nearly invisible hooks, watching for hooks in the air, watching the dank walls, the poorly lit floors littered with dozens of clawing hooks...
Ahh... but the wire is timed, you see. If the victim doesn't move after a few minutes, all the hooks merely pull back with incredible force, including the one latched in his face in the first place, tearing a huge portion of his face from his skull, most likely taking whatever remains of the nose, the upper lip, and the eye with it. The rest of the body soon follows and the creature basically explodes outward while retaining basic skeletal form. Death is now certain, with the creature visibly missing half a face, and most likely huge portions of its outer body. And even better, since he isn't actually missing any vital systems, his friends and himself will think they have a chance! "If only we can stop the bleeding" they say! "You can make it! Let's get out of here!" they exclaim... but ah... such fools. You cannot survive when most of your body is missing. The victim will die slowly, and he will pass away in sheer, unbelievable, unstoppable pain. He will die thinking he has a chance, that he managed to escape the trap alive. It's beautiful.