a little more on Complex Motor Stereotypies: i get excited and it comes through my body

In an interview with Joe Cocker:
Q:  "Where did your unique dancing style come from?"

A: "You mean my arm movements?  I actually saw myself with Eric Clapton - you know you see all your old stuff on YouTube now - and I was horrified at myself, with my arms just flailing around.  I guess that came with my frustration at never having played piano or guitar.  If you see me nowadays I'm not quite so animated, but it's just a way of trying to get feeling out- I get excited and it all comes through my body."

another video when he was older