A urethral sound is a medical device originally used to keep the urinary tract open in men with enlarged prostates. The sound is a long, smooth rod, made from metal or silicone, which can either be straight or curved depending on type. People use sounds to penetrate the urethra both in solo and partnered play.
More About Urethral Sound
Both men and women engage in urethral sounding for a variety of reasons. Some enjoy the feeling of penetrating a part of their body that is considered "unusual" or "different." Some enjoy sounding specifically as part of a BDSM dynamic. For men, sounding can access their prostate in ways that no other type play can.
A variety of sounding kits are available with sounds of different shapes and sizes. It is important to start with the smallest sized sounds in the kit and work up to larger ones. Sounding should always be performed with sterilized sounds and a lot of lube. A sterile lube should also be used.