My baby has always had strong legs and a couple of weeks ago started to straighten his them rigidly during nappy changes, making it hard to put his nappy on, not sure if he thought it was a game but it was quite funny (and difficult!) However now he has taken to kicking his legs out and literally slamming them down into the mat as hard as he can. He doesn't seem sad or happy when he's doing it - not sure if he's playing, doesn't like his nappy changing or is just doing it for attention? I get the feeling it's more of a frustrated thing but not sure. It doesn't matter whether I'm talking, singing to him or not making eye contact at night. Other than making it impossible to put his nappy on straight I don't really mind, but I'm worried he's going to hurt himself as sometimes he ends up moving himself and slamming his feet into the wooden edge of the changing table. There's not a lot of room to keep him in the centre of it any more! Any ideas why he's doing this and how to stop it?