I needed to tap a source of water to create a nice waterfall in my dining room. Everything was prepared: the waterfall would fall through the dining room, and then a channel under the dining room led off the side of the map through a fortification. All I needed to do was open the wall of the tunnel which was touching my water source.
Feeling too lazy to channel in from above (and slightly evil), I decided to go ahead and sacrifice a dwarf for the effort. I had the dwarf wall itself in and then open the wall. Two seconds later multiple bad things were revealed about this decision:
The dwarf was a mother carrying around her small child.
The water was under high pressure.
I had forgotten to make a floodgate to stop the water if needed.
The water shot out of the wall, instantly killing the baby and smashing the mom against the wall of the tunnel. She was dragged along by the water, fell down the waterfall and was pushed up against the fortification on the edge of the level with two broken legs and a bruised spleen. The baby's corpse was caught under the waterfall right underneath the dining room and wasn't going anywhere. The mother kept trying to run upstream but was unable to.
I felt pretty bad at this point. But thinking there was not much I would be able to do since the mother would certainly die soon anyways, I just tried to quiet my bad conscience and focus on other things, awaiting the inevitable message the mother had died.
A day later the baby's corpse started to fill my dining room up with miasma, making me have to wall out the waterfall to keep my dwarves from vomiting. Quite poetic justice, really: the stench of death was on my waterfall.
I was still waiting for the message that the mom had died. It didn't come.
After a week of game time or so I looked to see what she was doing and my jaw hit the floor. She was FISHING. The mom was fishing to stay alive while drinking the water. She was in an obviously really bad mood having witnessed death and the decomposition of her child. But she was barely staying sane because she was being "comforted by a lovely waterfall". That did it for me. I finally decided to launch a rescue mission to save her. Not 2 seconds after I had given the command to dig a tunnel to where she was, she went insane and died of thirst shortly after. I was too late.
Her name was Môsom.