That's it slave, feel the sting. Now take it a level further - grab a wooden spoon and begin whacking the side of your shaft from alternating sides. Left-right-left-right, etc.
Make sure every impact makes a sound and you're not allowed to hold your cock with your free hand to ensure it does because you should still be holding the balls rope downwards. If you're not, do so immediately and give yourself another 25 ball smacks as punishment.
I want to see 15 whacks on EACH side of your cock with the spoon.