Hi LMB, I'm not sure why they do it, but I know my son, and several other bubs in my mums group also did this, so I think it's pretty normal. Hudson would sit by the wall or coffee table and just bang his head back and forth on it lol! He's 2 now and has grown out of it quite a while ago. Just a stage I think? Although now at 2 if he bangs and hurts his head or something he will re-enact the accident just to see if it hurts again LOL! Kids do funny things when they are learning about the world.