Rusty & Sophie play all the time too. He is 7.7 lbs (7mnths old) & she is 1.6 lbs (14 wks) and I just WATCH carefully to make sure he doesnt get TO rough with her. She REALLY enjoys playing with him and just growls at him like she is bad @$$
Matter of a fact they are under my chair RIGHT NOW barking, growling, talking & playing with each other.
P.S. Sophie & Rusty's ears also go down (in excitement) when we get home