Recently I found out that arachnotrons make a passive growling noise while walking around. It's one of the sounds that can be played when you press Y to confirm that you want to quit the game. I could never pick this out from their foot stomping.
To me it would make more sense if they had no passive sound and this was their "injured" sound.
Would it be difficult to modify this in ZDoom?
If you give a monster zero or negative health with dehacked, you won't be able to hurt it with weapons, but it will vanish with the slightest tap from a closing door.
Kind of logical, but I'd just never thought about it.
Edit: The attached zip contains a deh file to set the imp's health to zero, and a few demos on Doom2 map01:
vani_imp.deh just shows the exit room imp being vanished.
vani_im2.deh has the player being squished under the door too; seemed only fair.
rvan_imp.deh shows that the "vanished" imps do respawn (when using -skill 5 or -respawn) despite not being counted as kills.
rva2_imp.deh shows the exit room imp respawning within the player's body.
vani_imp.zip