I prefer to think of it as "without blemish, without anything to be ashamed of". But hey, that works, too. It _really_ wasn't our fault the liaison insisted on walking into the grinder.
Honestly, the pathing of friendly units is just awful - when a path into danger is blocked, they'll still walk up right to the locked door and bump their heads against it before re-pathing. And if there's an alternative way to the spot just behind the door (especially if that path leads right through the danger the locked door is supposed to keep them safe of), their re-pathed algorithm will lead them through a huge detour just to get to that spot. They must be forcefully prevented from suicide.
I've tried out the glitched contact-free minecart grinder and that one works very nicely, too. Took care of five forgotten beasts.
Design, seen from the side:
#.._R#
#▲▲#
#_#
###
# = wall
. = open air
▲ = track ramp, upwards, bottom is solid floor
_ = plain floor, _not_ track. Can be smoothed or rough.
R = Roller pushing west
It uses the "minecart collision through solid floor" bug to pummel anything passing through the corridor below without putting any buildings in hazard. The double-ramped pit makes use of the ramp bugs to lift the cart back out of the hole and out east onto the roller, which pushes it back west. The non-track floor just east and up from the pit makes use of the oddity that carts coming from a non-track tile will jump over pits with track ramps just like over ordinary holes in the floor. Thus, the cart flies over the pit, collides with the wall and _falls_ into the pit. The fall triggers the indirect collision bug. I have ten of these in a row, consuming a pitiful twenty power - a lowest-power windmill could run a seven-roller array, which should already horribly murder anything smaller than an ogre. It delivers one beat per twenty-two game steps. I'm using copper minecarts, which are probably better than wooden ones, but a fleshy or gem-ish forgotten beast can take two or three pages of hits to go down, flimsier types expectedly get one-shotted.
In other news, most of the recent goblin-and-troll siege got bridge-crushed out of existence, but four stragglers are sitting around immobile doing absolutely nothing. That's the downside of this type of defence - goblins don't realise their squad is decimated and won't flee, but won't advance either, because they wait for pathing advice from their no longer extant squad leaders and mates. Even getting hit with a ballista arrow doesn't trigger the flight reflex.