My Mistress Friend and I have tied two of our slaves together by their balls, back to back. So everytime they tried to reach our feet, the knots on their testicles tightened and the short cord pulled the slaves back painfully. They were eager to lick our shoes and our feet so the more they tried to lick the more they inflicted pain each other. We started gagging them pushing our gorgeous feet deep down their throat pulling their heads towards us with the other foot. We pushed and pulled so the pain in their mouths was the perfect complement of the the torment of their, now blue, balls.