Izzy is prone to doing damage with her horn. Purely accidental, of course, but the combination of her natural clumsiness and her unnaturally long and pointy horn make her a danger to all things sentient and inanimate. Then one day, her problem is blunted solved.
[EDIT]: This was written WAY before the movie came out and based solely on the released still that included Izzy with the tennis ball, so it was pure speculation.
Rated Teen for some minor blood and brief sexual references.