The problem with the brain removeal thing was that the game crashed before they could die. Which is not so helpful.
My map doesn't seem to have any zombies. It's an evil biome, but all it'll spawn is skeletons. And mostly skeletal carp and groundhogs and occasionally wolves, who all seem to die the moment they're poked.
I did have a number of caged crundles--earlier I'd modded them to have the [PET] tag so I could tame them and slaughter them. I just got fed up with the fact that the cages would pull half a dozen crundles every time i managed to empty them. And that they'd occasionally escape the cages and run around the fortress cancelling everyone's jobs.
Yes, temperature is on. I think there's some weirdness going on with the temperatures of existing creatures, as opposed to new ones--and I'm guessing the crundles that were appearing on the map after doing this were still part of an existing pack, so their body temperature was already set--because when I opened up the arena after messing with the homeotherm of elves, they'd either spontaneously freeze, burst into flames, or, for the creepiest example, have their teeth, and then face, melt, followed shortly by complete evaporation if they were ever exposed to water.
(For those wishing to replicate melting elves, give them [HOMEOTHERM:10000] and [SELECT_MATERIAL:ALL][MELTING_POINT:10020][BOILING_POINT:10020]. It will also cause them to evaporate when killed.)
...and for some reason my arena was raining. So they didn't even have to find any water to melt.