tie some rope around your slaves balls. did your slave like pain? if he did here is an opputunity to find out how much.
Don't worry about tying it too tight, as long as it doesn't put preasure directly on the balls its not going to hurt much.
now is the time to find out how much pain your slave really likes.
it will be very valuable knowledge later.
try a few light slaps, twist his nipple clamps and so on. but don't give his cock any attention. We want to know if he gets excited without you touching it.