
Plot hole: There are six metal bars mounted around the circumference of the water wheel's axle. In the wheel's interior, when Jack frees himself he lands on his feet, begins to run and promptly hits his head on one of those mounted axle bars, then falls out. Moments later, when Jack returns and runs in the wheel, he is shorter (way more than a foot) than all six of the mounted axle bars spinning with the water wheel, which would make that previous shot impossible, however humorous it is. (01:52:40 - 01:53:55)






Answer: The jar was to put Davy Jones heart in. He can't touch dirt ever again since he failed to keep up his duties which means he wouldn't be able to get his heart back.