I just witnessed the gentlest hammering ever.
My current mayor, one of several dozen children of the Countess, who recently replaced an adopted Ancient Vampire as mayor of the fortress, has developed an unfortunate habit of mandating Bismuth items to be made. Bismuth is a nearly useless metal since it can't be made into anything, so the only way to meet this mandate is by smelting bismuthine ore into bismuth bars. Even with major mining projects and importing bismuthine from the trade caravan, I couldn't keep up with the mandates.
So I let the latest mandate fail. I figure it's no big deal - previous mandate failures have only resulted in some random hauler getting a vacation in my luxury prison cells for a while. The mayor will be pissed off, but screw him anyway. So when the mandate expires, and I check the justice board, I'm surprised to see that the mayor has picked the best metalsmith in the fort, and not for a jail stay but a hammering.
Now, I like this metalsmith. He's already a legendary metalsmith from making one of the fortress's most valuable artifacts, and I've spent years training up his blacksmithing skill cranking out bins and barrels so when the queen arrives he can make masterwork furniture from precious metals for her. He's one of the more valuable dwarves in the fortress, and one of the first immigrants, arriving in the first batch after the initial 7. I'm not happy about the possibility of seeing him killed or crippled for life.
Luckily, I seem to have one of the most apathetic hammerers ever. When the call for justice went out she was attending a party, and had no interest in leaving the party to do her duty. When she finally did tear herself away, it was to get a drink. Finally she went and grabbed the metalsmith, dragged him to the prison suite before deciding to go sleep. The metalsmith was mildly upset over being confined, but the masterwork roast and well-decorated bed in the prison made up for that. Finally the hammerer woke and returned to the prison to administer the punishment. I watched, waiting to see what would befall the metalsmith.
She went to the chained prisoner, and then a few moments later they both walked away. No blood splattered or body parts flying. I checked his wounds page - not even a bruise. The justice page said that no further punishment was needed, the hammerer had happy thoughts about having administered a hammering, and the metalsmith had the bad thought from having been beaten (which was vastly outweighed by the good thought about having been freed from captivity), so the hammering had clearly taken place.
I can only figure that the hammerer realized that the sentence was unjust and deliberately gave the weakest tap possibly with her hammer. Either that or the blows from an inexperienced hammerer who has probably never used her hammer in anger before didn't have much effect on a dwarf who's spent the last 30 years working nonstop at the forges. In either case everyone's happy, and I'm keeping this hammerer around since she seems to be the least effective executioner ever. The mayor, on the other hand, may have an unfortunate accident coming soon.