It was a very unsettling experience. I didnt realize she still had that vibe on her clit as it was under her pajamas and held in place by her panties. I delivered a playful but firm slap, and I felt the end of the vibe in my palm as it drove HARD against her clit. Her knees buckled, and she wailed like nothing I've heard from her before as she sunk to the floor in a fetal position. She was hysterical, and it took quite some time to calm her down enough to inspect. We paid close attention to it and avoided aggravating the area for a few days (much to her dismay). All is well now. I don't know if any other Doms here have had 'accidents' while playing, but I can say that its a miserable feeling to know that I hurt her.