Revealing mistake: There are brown pieces of paper that the brother has supposedly been writing songs on (when his sister is in the room cleaning). She picks up the papers and starts to sing, and he flips one of the pieces over as if they have writing on both sides. Only there is no writing on them, even though she is singing the lyrics he has written.
Revealing mistake: When duck and his sister are singing with the toy props, when duck's part comes we can hear the audio, but his lips are not moving.
