Sounding (for sexual purposes, anyway) actually is supposed to refer (though it does get bastardized) to urethral penetration with medical sounds. Sounds are actually medical devices (though I've never tried to find out what they're used for). I've seen them for sale in medical catologues. A good deal of the men who have talked to me about it have admitted to having nurse fetishes and/or nurse fantasies involving sound play and other forms of urethral torture, including the addition of a tens unit to send electricity along the sound, and stuffing the urethra full of q-tips coated with mentholated balms and spicy substances. I have heard of sound play mostly refered to as urethral torture. I would never participate, and do not kow whether play or torture is the more apropriate descriptor.