the trick is to pinch their nipple so hard (must not forget the
twisting of the nipple), that they are in the anguish of utimate
pain/laughter.
the guaranteed reaction is that they will freeze, pout their lips
and try to whistle.
the 2nd trick is to run as fast as you can once you let go.
Strangely, the girls love it. No matter how much i ask them to
whistle, they just moan.
