SRD:Improved Unarmed Strike
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Improved Unarmed Strike [General]
You are considered to be armed even when unarmed—that is, you do not provoke attacks of opportunity from armed opponents when you attack them while unarmed. However, you still get an attack of opportunity against any opponent who makes an unarmed attack on you.
In addition, your unarmed strikes can deal lethal or nonlethal damage, at your option.