Jenny Mace slaps her own breasts really hard, a lot. She makes a good face when Tony tells her that's what we're doing next, but starts right in. First she slaps up underneath one at a time for a while so they bounce spectacularly, then switches to an alternating rhythm back and forth (which she says felt very silly, but I think looks hot), then finally to slapping really extra-hard down onto each breast over and over. That last one particularly looks like it hurts, and her tits are impressively red afterwards.
