Pink,
I don't know. I think if you tell him the chances of it inadvertently happen again may diminish. He may be more cautious in the future. If you liked it, and want it to happen again maybe keeping it to yourself would be a good idea.

However, if it is important to your treatment that he knows everything, then I would disclose it. I think your own training in this area could tell you if it is something clinically significant.

Since I'm living vicariously through your therapy my question for you is...Did he have big hands? ;-)