Iwata: I see. Uchida-san, how did you come up with the sound for the bubbles?

Uchida: We wanted it to feel different when you’re in a bubble, so we made a voice come from the Wii Remote. The first time I saw a bubble on the screen, it was drifting around as if it were saying “Lemme out!” so we had a voice say “Help me!” while a player is in a bubble. But later I learned you could also put yourself in a bubble. I thought having the Wii Remote say “Help me!” was a little strange for someone who wanted to stay in the bubble.

Full Interview Here