I was *trying* to play Mario and Luigi: Bowser's Inside Story when I got to the part where you can go practice your new move. The only way to exit from that screen is to hit the left shoulder button.
...which doesn't work on my DS. This explains why I could never figure out how to rotate pieces in Scribblenauts, too.
Very few games use the shoulder buttons, but... well, M+L:BIS is unplayable without them since you get to that point in the tutorial and have no way to move past it.