You see, the trouble with executing goblins en masse is that, the moment a dwarf stops dragging a goblin prisoner by his nose and actually gets around to throwing him into a pit, any nearby dwarves are immediately scared shitless by the free-roaming goblin, even though he's totally harmless down in that pit he was just thrown into. This can get annoying when you're trying to design a successful deathtrap, so I've been trying to find a way around this for a while now. The only partially successful design I've come up with so far looks something like this:
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+#^D Trap Room
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= Wall
+ Floor
# Floor Hatch
^ Pressure Plate
D Door
Goblins are dropped onto the floor on the left from the z-level above, move to the right, and step on the pressure plate, which opens the floor hatch. I used the one-way floor idea originally suggested
here to make sure that goblins can't move back the other way once they move to the right. To the right of this hall would be the actual trap room, with an animal chained behind a fortification to lure them in. It's obviously not perfect since there are still places the goblins can stand to prop the door open or avoid the trap room, not to mention fall into the pit under the floor hatch. Still, it assures that dwarves won't be scared off by recently pitted goblins.
...My design sucks. I didn't just come here to show it off, I want to hear your ideas on the subject. How do you design your traps to avoid spooking your dwarves with previously pitted goblins?