Flutter is a mute Toon, as it is shown that she cannot speak other than in '..." or "..!" This doesn't mean she can't make noise however as shown in Shrimpo's interaction with her when he says "I HATE HOW YOU'RE SO LOUD!" Though this could be an overreaction on Shrimpo's part. Also, a lot of Toons seem to understand her as in their interactions they react accordingly to the other dialogue Flutter has said. Despite this, she is kind and a good friend towards the other Toons, trying to be helpful.