Lady Scarlet wanted her slave to cry and she was sure that if she did something she had never done to him, he would not help but cry. She did not want to use a method he was used to as it would not be as effective as something new. So the mistress bit his nipples and made him not only cry, but also fart and also pee his pants.
Mistress Zora wanted to toughen her boyfriend and she wanted him to start by being a little bit tolerant to pain. So she bit him a little bit and as he struggled to endure the pain, she increased it a little bit. They did it a few times and he started to get the hang of it before she decided to bite him harder. He screamed out loud until she stopped.
This mistress wanted to be pounded like never before but this guy could not do so as he was a premature ejaculator. She had to show how disappointed she was with him and in doing so, she bit his dick to make sure he knew the extent of her disappointment. He was in pain but he understood her better and he realized that he had to work on his staying power.