Origin of the bone crossbow
I drafted two dorfs into the army, pretty standard procedure. Decided to have them spar with each other so they wouldn't suck in an actual fight. Now, I was pretty new to the game at the time, so I didn't realize that my dwarves had both picked up iron spears instead of wooden weapons. The result, of course, is that one of them was mortally wounded.
The wounded dwarf was taken to a bed, but he was in pretty bad shape so I figured he would probably just die or something eventually. For several months he lay in that same bed bleeding to death, but he just clung on. Then, one day, he miraculously got up.
While his body was healthy, however, his mind was not. Apparently lying in a bed in excruciating pain for several months makes dorfs go a little crazy. He ran out into the hallway and killed some poor guy's pet (it was a donkey or something). Now, I figured that for this dorf there was just no going back, so I had the army go in before he killed anything else.
Obviously, the troops made short work of him. But who was the one who struck him down? As you can expect, fate was cruel — it was the very dwarf who had wounded him in sparring and caused his condition in the first place.
Now at this point, I was shocked. But the story doesn't end here. The miserable dorf who had wounded his friend and comrade, and then killed him, was having some pretty unhappy thoughts about the whole ideal, as one might expect. Fearing that he too would go crazy, I removed him from the army so that he wouldn't be carrying a weapon if he did. Meanwhile, a local crossbow-maker entered one of those strange moods. He went down to the crypt, where I had neglected to make enough coffins for the recently deceased dwarf to be properly buried, and found his body lying on the ground. Out of his bones he made a crossbow.
Upon witnessing this, I immediately placed the dwarf who had killed his comrade back in the army, and equipped him so as to be sure he got that very crossbow. For many years, he battled the enemies of the Fortress, remembering with each shot from his friend's bones the terrible price of reckless sparring.