People familiar with dogs know that some dogs will start shaking a leg when you rub them in a certain spot.

I have been unable to find this spot on Dipper.  

In fact, he found my spot, because when I was poking around him for the leg shaking spot,  he started licking me, and when he licked my ear, that made my leg shake.

I find this reversal of fortune disconcerting.  I would like to know where the leg-shaking spot on a Corgi is, and would appreciate a link to a diagram or video that would reveal the shake-a-leg spot on a Pembroke.