Michael loves to mimic Katie, which means squealing, blowing raspberries, and all sorts of fun things. But he is also a great teacher, and takes advantage of the fact that she is a captive audience to teach her from his vast reservoirs of knowledge.
Copying Katie rolling onto her tummy
Showing how Katie plays with her feet
Practicing their swimming strokes
And I caught Michael teaching Katie some sign language. Michael has little stars on his shirt, and he would point to his star, say "staaaaaaaar!", then show her the sign for "star." It was so precious!