The Nipple Pain Test

Lets see how noisy my slave can get when I test my high-heeled slippers on him. I have chosen some of my boots for this experiment in slave volume. Which shoe soles and heels inflict the most extreme torture on his nipples and cause him the mosst pain? With which of my mean shoes will make the slave scream the most loudly? I will find out now by totally fucking-up jis nipples!