This is so wierd. I had this conversation the other day. In Stranger in a Strange Land (source of the word), Jubal Harshaw first figures out Michael is telepathic because Jubal asks him to scratch his back, and Michael scratches where it itches. That, for me, is the essence of grokking. The sharing of sensation, thought, and understanding.

I have shared this sort fleetingly with people many times. It is rare that I have experienced it on a consistent basis, though it is possible with work to open to each other in such a manner.