Random little things in the games

Ok, so I was playing Pokémon Black and opened the summary page for the Party. I tend to tap the screen when I'm not using it (out of habit) and imagine my surprise when the Pokémon hops around and shows the backsprite. Totally random, but amusing to me =P

I wanna know other random little things they put into the games that I may have missed. This includes prior generations, so feel free to post things like how X may do something amusing if you do Y first in Red. Just make sure they're relevant and feel free to discuss the random things here.

Discussion of this subject for Black & White is pretty much covered by this, but feel free to discuss other generations here.