If your perception skill is high enough, you might notice something about the bullying NPCs in the Temple of the Moon on Emerald Isle. You may note that even though they want you to hand over your lovely hat (and then the rest of your clothes) and will attack if you say no, they are still considered "friendly" people, and as such are green. Yelling works on green folks, so you can yell them all around the temple. Also, yelling is about the only way I can think of where you control the face reaction of your character(s) at will. The reactions change when you're afraid, or poisoned, or falling from a height, etc. but these only occur under certain conditions. No matter where you are or what you're doing, you can always yell, and so always cause a reaction.
