I once set up a trap that involved a room with musicians playing dance music. Anyone who entered the room and heard the music started dancing, and didn't stop. Fulfilling the quest required passing through the room. The musicians were demons that were impervious to everything except fire -- but they looked like nice, normal humans. "Burn the musicians!" became one of the ongoing jokes of our game, used in situations where the only life-saving action was one that would normally bring lots of bad karma. Both our other DM and I were big on hard choices.
JP