Is anal fisting safe? Will you be able to go back to your original size afterwards? This looks to me like it could cause some control issues. I've seen a clip where a girl had nearly her entire arm in a guy's bum! The anatomy books I have don't show a straight digestive system. What about vaginal?
Rosebuds?

Sounding? I get the insertion side of it, but stretching? Is that permanent?
Ball and pussy stretching? Is that a temp thing... I wouldn't want my balls hanging out of my shorts at the gym.
And there's many other things I can't thing of at the moment (feel free to chime in with one).
I'm not saying I would or wouldn't do any of these- I'm just a curious guy and would like to know.