Urethral play, or Sounding, is the practice of inserting a sound (usually a long thin rod made of surgical steel) down the urethra towards the bladder. Sounding can provide heightened sensation and pleasure.
It's more common for people with penises to engage in sounding, though people with vaginas can also participate in sounding. Of course there's a vast anatomical difference between the urethras of people with penises and vaginas since vaginas have shorter, differently shaped urethras.
Sounds

Sounds can technically be anything that's slender and that you want to insert into our urethra- forums indicate a wide variety of items from thermometers to knitting needles to toothbrush handles, but all of these carry risks that surgical steel sounds don't. Surgical steel sounds don't carry the risk of breaking, are easier to sterilize, and won't cut you.
Sounds come in two primary shapes- Van Burens which are curved, and Dittels which are straight. Sounds that are intended for dilation of the urethra are called Pratt and Hegar sounds.
Some sounds also are textured to add to the sensation.

Why Do People Like To Stick Things In Their Urethras?
Just like any other sexual practice, people do it because it feels good and they enjoy it.
Its a different pleasure from a hand job. It's a very intense feeling.
The stimulation of the prostate (for people with penises) through the act of sounding can be very pleasurable. The route of the urethra crosses right through the prostate.
The urethra itself is highly sensitive and the act of moving the sound in and out of the urethra slowly can be very pleasurable and lead to orgasm on its own.
The taboo of penetration of part of the body that isn't meant to be penetrated can also be very kinky for some, adding to sexual arousal.
Sounding can also add to the sensation during other sexual activity such as hand jobs, oral sex, or masturbation.

How Big Are Sounding Rods?
Sounds vary in size, especially when you look at Hegar or Pratt sounds which are meant to enlarge the urethral opening. Typical sets with multiple size sounds range from 6mm to 12mm in diameter.
What Are The Dangers of Sounding?
The urethra, like most internal parts of our body, is made up of delicate tissue, and injuring it can lead to a urinary tract infection. Its important to use clean sounds and sterile water based lubricant. You should also urinate soon after finishing urethral play to flush any foreign material out of the urethra.
Its important to use smooth, shatter and break proof sounds. Never use force to get a sound to go further in. Work your way up to larger sizes.
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