Stimming

.. or "self-stimulatory behaviour" has been much discussed by psychologists, academics, carers and autists themselves.  Google returns 627,000 links on the subject. 

For Corrie it's clapping, and it means he's really enjoying himself.  It can get a bit loud sometimes, and I feel mean discouraging it, but sometimes it's nice to sit next to him and be able to hear the telly!!  It's wonderful to see as well sometimes, because it tells us he's having a great time and really connecting with something.