Josh loves to play Wii sports, and Lucas loves to play along too, but doesn't know how to push the right buttons to actually control the Wii. So we've discovered that tennis is the best game for Lucas to play along with. Josh plays the computer, and Lucas is sure he is controlling the movements of the other side. He doesn't even have a Wii controller, he has the TV remote or, in this instance, a drumstick. But he jumps and swings his "racket" and thinks he is playing. At around 0:24 in this video, you can also hear his Seles-like grunt. It is really quite cute.
He also has the Wii racket accessory (sans Wii controller) to further the experience. Maybe he has a future in tennis, he sure seems to love it!
