Good evening girls. My son is 9 months old. Lately he's been shaking h…

Good evening girls. My son is 9 months old. Lately he's been shaking his head. Could this mean something? Or is it normal? He sits and shakes his head by himself. Has anyone had this happen? Maybe he just finds it interesting ?‍♀️ Nobody scolds him, there are also no arguments, he's surrounded by care. But sometimes he hits his head against the door or cabinet.