Hi. 
I think this may be one of those things that someone else has to do to someone. ‘Cause I’m not gettin’ any action by myself.
I’ve tried this with and without pants on. With my fingertips and my fingernails. I’ve tried several spots on my thigh. I can’t find any place that forces this reaction.
And how are you explaining it to your co-workers? 
Beat me to it 
Re: the OP, the ball-crawly action cracks me up every single time!
I sense a new entry in the annals of pick-up lines least likely to work.
Well, that explains why people were edging away from me on the subway today…
That does it. I’m not letting you outside by yourself anymore.
Does this work through clothing or instead require a more sensitive touch, because I won’t be able to see my girlfriend for about a week.
Well, learn something new everyday. I just asked mrsin about this and he says it happens when I stroke his right thigh, but not the left. Have to look next time. 
Woops, that last message was from me, not the sinkid. Nope, nope, nope sinkid is not stroking his dad’s leg at night.