If you look up "ball" in DS Rakubiki Jiten (the DS Dictionary), you are presented with two words. Tap the grey one and, voila, up pops the old Game & Watch title Ball. Or, for a less involving surprise, look up "Nintendo" - tap the word and you get the little Mario coin sound.

Neat touch, Nintendo. Very cute. Luke Plunkett

Game and Watch games buried in Nintendo's DS dictionary [Siliconera]