My ho yin is like that too.
He is so excited when he plays with daddy (laugh everytime).
when I play with him, he seldom laughs (I need to try very hard to make him).
However, when he tries to 扭訓, he only wants me to hold him (very tired but enjoyable).
I think he knows who can be "ha" coz daddy wont let him "ha".
Very clever and "ko wa"!!