That was the 15mm sound. My kit goes up to 18mm. When I first started, was at 8mm. Tempted to try the u-shaped sounds to see what it's like to enter even further. With <=13mm, the entire sound can easily slide all the way in, but I never let it go too far - less I wind up as one of those cases in the ER where I somehow got a sex toy stuck inside me.
Finally reached my bladder today. Got a lengthy rod and got it past the curve. It's quite a different and thrilling experience. Will try to post a cell phone video I took tonight, if I can find a good way to post it.