Okay, here's one for the guys!!

This teaches overcoming pain. This teaches conscentration while in task.

First prenegotiate a reward because you want her to consentrate and that reward is what she is looking forward to. Let her know that failure to achieve a task will mean she is to be punished in a way that you see fit.

You stand and she kneels at your feet. You are holding a crop. Instruct her to lick your balls like she loves them. You lightly tap her bum with the crop over and over and be consistant. Then you instruct her to take your left ball into her mouth and suck gently. Increase the slap of the crop. Remind her to concentrate on the task. She may not bite no matter how bad the pain is. Then instruct her to go suck your right ball and again increase the pain. Finally instruct her to take in both of your balls and do it without using her hands. Give her more pain than before.

What she will learn is that she is able to take far more pain than she thought she was capable because she is concentrating. She will learn to listen to you and to concentrate on what you say. This is an enjoyable task for both people!