I nearly fell out of my seat when I heard what Ramachandran said at 1:30.  He talks about mirror neurons:

When we reach out for something, motor neurons fire.  When we watch someone else reach for something, those same neurons fire, mirroring the action that we see.  So we are essentially passively practicing when we watch someone else perform a movement.  I have, for some time now, been an advocate of using video for rehearsing stage fighting.  This information reinforces this practice, as the more we watch the action, the more we are passively learning it.  As an extension of this, the more we watch well-performed actions, the better quality our own performance will be.

Ramachandran also tells us (4:40) that a sub-set of neurons also fire when we see someone else being touched.  In fact, the only thing keeping us from experiencing this touch as a fully physical sensation is that the touch and pain receptors send a “veto” to our brain, saying that, no, you yourself are not feeling this sensation.  As a an actor and fighter, this says to me that the more truly I feel/perform my wounds, my exhaustion and even my shying away from an incoming sharp and dangerous blade, the more I draw my audience into the action, both on a mental and nearly physical level.