The first time you play the game in a particular web browser, you should always see the singing panda upon completion of the first game. You may have to click the Play Panda Song button to do so. However, after that you should only see the singing panda if you win by 50 points or more. You can do it!
(Note: "First time" is kept track of in your web browser's cookies. If you clear your cookies, the game will be treated as though it's your first.)
(Another note: If you are playing in a browser where sound for this game is not supported (primarily the built-in browsers of many mobile devices) then the game won't show the Play Panda Song button at all.)