Continuity mistake: At approximately 15 mins and 15 seconds, Max is looking over the image and info on the activity for the Avatar drivers. When Jake first drives, he is wearing a black "dog tag" with a blue spot. When he walks over toward the viewing window with the portable screen at approximately 15 mins 30 seconds, the "dog tag" is orange with a spot of black. (00:15:15)
Continuity mistake: In the scene where Grace is talking about the Tree of Souls in the mobile lab, Trudy stands behind Jake with her right hand on her hip and left hand hanging down. After grace says "Outsiders are strictly forbidden," we are shown a close-up shot of Jake and hear Grace continue with "You lucky swine." In the background, we see that Trudy has suddenly turned 90 degrees clockwise and is apparently supporting herself with her left arm on what seems to be the same table Norm is sitting on. (01:12:00)
Continuity mistake: In the scene where Neytiri and Jake are standing under the Tree of Voices and Neytiri says to Jake, "This is a place for prayers to be heard", Neytiri's queue is at her back. In the next shot it is hanging over her right shoulder. (01:18:45)
Continuity mistake: When Jake is recording his first video log entry, he moves the recording camera around a little to get a better view of his face, and is looking directly at a screen to his right to see if he's centered his face correctly. In the very next shot, he is staring straight forward at the camera. (00:10:10)
Continuity mistake: In the scene shortly after Neytiri saves Jakes life in their first encounter and Neytiri knocks Jake down she is holding her bow with arrows. When the shot changes the arrows are gone, and when the shot changes again they are back. (00:44:00)
Continuity mistake: During Jake's first video log, Dr. Spellman and Dr. Patel are leaning on a table. When the camera changes and Jake turns his head over his shoulder to ask the two doctors a question, Dr. Patel is much more leaned over than before the camera change. (00:13:48)
Continuity mistake: When Jake is trying to catch up with Neytiri, they get ambushed by Tsu'tey and his posse. Jake pulls out his dagger, but then throws it down to save his butt. He's surrounded. So he has his arms out where they can see it. While Neytiri is confronting Tsu'tey, Jake is in the background with his arms spread out, and his dagger back in the holder. (00:42:10)
Chosen answer: The Core didn't originate the name - it's been used since the 50's and even has its own Wikipedia article at http://en.wikipedia.org/wiki/Unobtainium. There it's described as "any fictional, extremely rare, costly, or impossible material, or (less commonly) device needed to fulfill a given design for a given application."
Jon Sandys ★