my son is going through the same, he's 22mths now.He hurt his hand when he was little on a piece of glass, we taught him this was and "ouch" and I would kiss it better for him, now whenever he does something bold or gets in trouble, or doesnt get his own way he wollops his hand of the nearest object and cries at me to say Im hurt kiss it better!!!
I think its his way of distracting me from the fact that he is being bold so he can get his own way, he has also slapped me in the face a few times and when this happens it straight into bed with no privileges, and a tap on the bum, I know time outs are a min per year but I tried that with the little guy, it didnt work he would come out and do exactly what he was doing to be put in there in the first place, so now it a simply case of when you stop crying and screaming you can come out to play, this worked, killed me the first few times and my partner had to make me stay out of the room, but he knows now the quicker he stops crying the quicker he can rejoin the fun, consistancy and stenght as well as been firm seems to be the best route, plus the odd tap on the nappy never did any harm. hope this helps.
binx