I freed the spiders in the goblin camp and they killed four goblins from Ragzlins group for me - very nice.
actually, that's how I do double Speak With Dead on mind flyer's corpse. Normally, if you trigger the hobgoblin use the speak with dead on the corpse, you can't cast it again. But when spiders attack, they are drawn away by combat, then you can sneak in do your own speak with the dead.
