the trick is that she must put her nails on your ballsack and not on the balls itself. once she know what she is doing even some sack scratching is great. and if she times the biggest pull RIGHT before you cum and holds it then this will turn you into a peter north if you know what I mean. EPIC shit.
And to repay her...the next time you have her on top and she is about to blow, make sure you have a very cold glass of ice water near the bed---when she is about to have a orgasm, stick you fingers in it, then stick them in her asshole...result, fun times had by all (she's pop off like a whistle)!
