Good Tit Torture method

Folks,
Found a sweet way to torture your subs tits that is very controllable, cause no damage, needs no special equipment and is agonizing--fingers...But, applied like this:

My wife sits up with her back to the wall or headboard and the sub is laid on her backwith her head in the wife's crotch facing up. Bind the subs wrists around the wife's waist affixing them at her back. I then kneel astride the subs thighs. The wife is then free to work the tits--sharp clean nails work worders and cause little damage that doesn't heal within a couple of days using nespoin or ointment of that ilk. Enjoyed it a lot--it's real intimate and with two Tops, the control of the sub is complete.