Thought i'd share since recently my experiences with urethral sounds have been at the hands of initiator of this thread - Mistress Ayn.

Initially it is the fear of someone putting something inside of your penis. Mistress Ayn made it more terrifying for me - showing me a ridiculously large sound - one that would never physically fit inside of me - and then blindfolding me. The fear level rose, yet Mistress Ayn would never harm a slave with more than s/he could physically take.

Yes, it is like how others have described - like being fucked inside your penis. There can be some discomfort but an expert Mistress and lube generally minimizes the hurt. It is not about pain, for this technique, but about the fear in giving up control and having Someone insert a metal bar into your penis.

i also found the after-effect of having to urinate, which can be a little painful, to be an excellent post-experience.

Safe and sane play can be a prelude to a fearful / satisfying session, one that i hope to repeat again and again.