Al eeped and dunked his head in, diving forward to avoid Severus' hands, thus putting himself firmly into Severus' grasp. His hair was wet now as he shook his head like a pup, splashing bathwater like a soapsud fountain.
They slipped and slid in the round cauldron, Al and his glasses ended up in Severus' firm, soapy grip. Al was twisting and turning his head this and that way to avoid Severus' wet, soapy fingers, not because he particularly wanted to avoid them but because the difficult way of washing up was so much more amusing than the alternative.