You could tell Jack Black was itching to act up. Sitting on the dais with four colleagues to promote their new animated film, "Kung Fu Panda," at a hotel in Shinjuku, the roly-poly actor looked — as he himself put it — like "the cat that ate the canary": face frozen in a self-satisfied grin except for eyebrows that elevated in response to something someone said. The expression he used usually describes the face of someone who has already done something naughty. But Black was contemplating doing something naughty, and he saw his chance about five minutes into the press conference.

"Now if you'd like to see some kung fu," he said, standing up. "I'm just afraid . . . well, where should I do it? I don't know official kung fu, but I'll show you my favorite pretend kung fu." He jumped on the table and mimicked the stance of the title character in the movie poster. True, it didn't look like real kung fu, but it certainly looked well practiced. "Now I need shiatsu massage," he said, retaking his seat.

His colleagues were as delighted by this typical Jables display of fanboy exuberance as the press were. Director Mark Osborne pointed out that Black, who voices Po, the panda with the martial-arts movie obsession, was more than just an inspired choice. "It's the best casting ever in the history of cinema," he said. "We took a lot of inspiration from Jack to create Po. He's a guy who succeeds in being like his heroes by being his own hero. I don't know what we would have done if Jack had said 'no.' "