Other mistake: When Michelle Rodriguez is flying the copter she doesn't have a mask on when they are at the tree of life to shoot down the tree. The machine gunner has his mask on. It's an open cockpit.
Factual error: During the hometree bombing, the "sky people" throw gas grenades at the N'avi. It's a cool tactic but because of the helicopter blades rotating right above them, the gas would just get blown away therefore making it a useless thing to use in the war.
Other mistake: During the battle between the marines and the Navi, colonel Quaritch shoots down Trudy's ship. Despite her cockpit having bullet holes in it, somehow she is still able to breathe. Unlike Quaritch when Jake sticks the knife into his AMP.
Chosen answer: Jake and Neytiri were holding hands and Neytiri had her hair unbraided. It is also possible that when Na'vi mate, their appearance changes slightly in a way that only other Na'vi could see.