Once, at an adult theater, I made a slave using a cage like him to cum sucking his cock. He was with his old chubby master and I wanted to suck the master's cock and eat his asshole. He told me, if I could make his slave cum sucking his cock in the cage he would allow me to do what I wanted. The slave probably was without cumming for weeks. I didn't suck his caged cock for more than five minutes and he gave me a huge load of cum in my mouth. After that I ate the master's huge and tasty ass for more than 30 minutes, until he decided he wanted to cum in my mouth. So he did.
We must reach the limit of tolerable pain without ever going further, but without ever going down. Only in this way can one have a perverse pleasure that transforms pain into sublimation.
The balls are perfect for these practices. Never complain.