There are two main techniques involved in causing the sensation of pain within the testicles. They are administering a sharp blow (as in punching/hitting/kicking etc) and crushing (as in squeezing etc). Personally I've always enjoyed striking my nuts with a sharp blow as this simulates the effect of being hit in the groin by a woman. It also causes a more severe wave of pain to wash through them (having said that, any man who has had his gonads squeezed by an angry woman will know how debilitating a good squeeze can be!).

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