When you get to a high enough level in Anticipation, you come across the Grey Squares which, if you land on them, put your piece into a kind of roulette mode to allow you to choose what color you really want, which is useful for wrapping up the game if you only have one color to go.

But! If you rapidly press A and / or B before your piece lifts off to start flying around all over the place, you can actually play a puzzle on that square

I don't really know why you'd want to, though, since you don't need any grey cards to complete the game.

Maybe you want to show off or something. And I'm cool with that.