What’s the attraction?
There are intense psychological effects in being penetrated in a body part as vulnerable and sensitive as the cock. With catheter play the sub surrenders control of one his basic functions: control over his bladder. He’s turned on by feeling humiliated and abused as the top decides when he can and can’t piss.
This kind of medical role play gets its power from the top exercising dominance over the sub, the fetishisation of hospital/medical paraphernalia and procedures, and their associations with control, authority, power, pain and fear.
Done correctly, inserting sounds or caths should mean no real pain. Discomfort is a sign of bad technique. The sensation can be intensely pleasurable and some sounds are even designed to give added electro stimulation of the urethra. Sounds gently moved to and fro once inserted can be a real turn-on. Sounds with a bend at the end (to fit where the urethra turns to join the bladder) are good at stimulating the prostate gland (the male ‘G spot’).
Repeated use of sounds will permanently widen the urethra, an effect some men want.