Causing pain, muahahaha: an old jiu jitsu favourite is pressure on the nerves behind the windpipe - reach around the windpipe on both sides and push diagonally up. It's tricky to find, but I'm sure you medical types will have no problems :-) Another good one, if they're lying on their back, is to press your heel into the nerve bundle on the inner thigh a few inches above the knee. Of course the army test for "are they really dead?" - back when I was a cadet, at least - was kick 'em in the nuts.