For you, playing dead is more than lying still and holding your breath.
Benefit: You can attempt to appear dead, slowing your heartrate and breathing considerably, blocking out reactions to pinpricks and similar stimuli, and lowering your body temperature. Entering this trance-like state is a standard action, and while maintaining it you are paralyzed (though you remain aware of your surroundings). In this trance you can hold your breath for one minute per point of Constitution score, which is also the maximum duration of your trance. You appear dead to all casual observers, and may make a Bluff check (opposed by an examiner’s Heal or Perception check, whichever is higher) to appear dead even to a careful examination. If you ready an action to use this feat when you are next struck for damage, the attacker must make a Perception check opposed by your Bluff, or believe it has slain you.
Adventurer’s Handbook: Genius Guide Volume 1