Specialized probe, that is inserted into the penis Urethra, that reaches the bladder.
This particular 'sound' is made for insertion into the bladder, through the Urethra, from the penis. Proper lubrication is required, as well as technique, in order to avoid injury.
This 'sound' has a very pronounced curved at the ends, to allow for passage through Cobbs Curve, that prevents direct access into the bladder.
The probe is used for stimulation purposes,
Originally made of glass, today's sounds are generally made from metal.
They come in various diameters.
They are primarily used in Medical procedures, to stretch the urethra, and eliminate some blockages, that can occur or strictures.