Choose items after continuing: After a game ends, hold down Select and hit Start to continue. After that you can use B to select which item you want to use as the game starts.
Secret message: There is a secret message lurking one line under where the NES's video memory ends. You can see it for a split second between "Get Ready" and the game itself, like this:
The fact that the game was programmed a year before it was released provides some of the explanation why this game was dated almost immediately.
