The Dangers of Nettlesteel

You've never been shot, have you? By one of those arrows? You know the ones I mean, most of the arrow is fine, a normal shaft made of some sort of simple wood, not a composite. Simple flight feathers, to keep it straight and everything. You'd think the arrow was normal, boring even. But then you see the tip, if you're lucky. Pale green and sickly, like the metal itself has gone mouldy, you can see the swirling forging patterns present in the arrowhead if you look hard enough. No wonder the rest of it's so basic, you'll say, they spent all their money on making a nice and pretty arrowhead. You think nothing of it, as you go to get the arrowhead removed by the camp healer. You might still think its fine when he tells you the arrowhead won't come out.
But then you see his face.
As pale as soft winter snow, he proceeds with caution, telling you how, if you don't disturb it, everything will be fine. This frighten's you of course, no sane doctor would ever say such strange things, but then...
It moves.
A stabbing pain bursts from the wound, like tiny little metal worms are burrowing their way into you flesh. The muscle around the site twitches and convulses, at once being frozen cold and burning hot. As the tendrils of the metal continue to work their way through your dying limb, a camp sergeant ties a tourniquet around your shoulder, elbow, knee, whatever, and with one fell swing of his blade detatches the infected limb.
You cry. You wail. You plead for it to stop. The stump is seared off with boiling tar and you are taken to a tent to rest. "Let's just hope none got into his blood" you here one doctor say, as you finally fall asleep.
So don't tell me you know pain.
You don't know nettlesteel.