She stands there waiting, watching, as you flick your balls as punishment.
First it doesn't hurt as you are gentle, she gives you no indication if this is good or not.
You flick harder and it begins to sting, again she doesn't move a muscle.
You are now flicking as hard as you can, each time sending waves of pain through your aching balls, still she says nothing.
"I can't do anymore." you whimper in pain finally.
"Good slave, that is enough. Now... think of me in that nurse outfit again." she smiles at your distressed look.