When Zuko and Azula are fighting on the ship, near the beginning of the fight, she scratches him with her nails, leaving a row of cuts on his face. In the next shot, the scratches are invisible.
When Azula fights Zuko and gives an evil glance down, her flame pin is missing.
When Azula fights Zuko on the ship, the first time she uses lightning technique it plays the Firebending sound instead of the electrical sound.