Continuity mistake: After the Flying Dutchman's attack on the Pearl, when the Kraken attacks the Pearl, one of its tentacles comes through the captain's stateroom stern windows, which has considerable damage - notably the left window and part of the wall are completely gone. When Gibbs says, "Abandon ship or abandon hope," the stern windows are actually more intact - especially the left window/wall. (02:03:50)
Continuity mistake: Throughout the film, Will's hair continually changes position between shots, such as hanging loose, then behind his ear, and back again, or vice versa; for example, when he holds Elizabeth's dress aboard the "bride spirit" ship.
Continuity mistake: When Cutler Beckett shows Will the Letter of Marque, the seal beside King George's signature is seen. Later, while Elizabeth points the gun at Beckett, he places his own seal below, and the shape of King George's seal is entirely different now. (00:11:20)
Continuity mistake: After the cage of bones falls into the water, Cotton reaches up out of the water to open the broken cage, but in the next shot he is still under the water, behind Marty. (00:40:45)
Continuity mistake: In the scene where Will visits Elizabeth in jail, she is rubbing his chin in most of the shots but in one shot her hand is suddenly down and then it goes back up again in the next shot. (00:18:40)
Continuity mistake: When Jack beheads the pirate and then when the pirate body searches for its head as Jack unlocks the chest, the plant debris appear and disappear in Jack's hair. (01:51:10)
Continuity mistake: In the row boat, on their way to Tia Dalma's, when Gibbs discusses the Kraken, the large tear at his shoulder is visible, as are other imperfections on the tattered vest. Later, the tear disappears and other things change as well. (00:47:10)
Continuity mistake: When we first see Jack as the "god," the multiple eyes painted on his face are sharp and defined. In the brief second shot, where we see the left side of his face, they appear worn and blurred. The third shot shows them sharp and clear again. (00:23:40)
Continuity mistake: When Pintel, Ragetti and the dog are in the boat, the corner of Pintel's collar is folded up when he says, "Aint that right, poochy?" and also when the dog jumps into the water, yet, it is folded down in the other shots. (00:29:15)
Continuity mistake: After Tia Dalma hands Jack the jar of dirt, the jar is positioned differently within Jack's grasp between shots - note the lid. (00:53:30)
Continuity mistake: During the dice game aboard the Flying Dutchman, when Will challenges Davy Jones, the cloth with the key drawing is folded and positioned differently between shots. (01:21:00)
Continuity mistake: When Elizabeth, Will and the rest watch from the long boat, as the Kraken takes down the Pearl with Jack aboard, in the shot facing the Pearl Cotton sits directly behind Will, but in the shot facing the long boat Pintel sits behind Will. (02:14:55)
Continuity mistake: After Will challenges Jones he is given five dice - one being considerably smaller than the other four. However, when Will looks under his cup during the game, all five dice are of similar size. (01:22:00)
Continuity mistake: When Jack shoots a hole in the casket killing the bird, the amount of feathers on the casket differ between the shots. (00:06:00)
Continuity mistake: At Tia Dalma's, the key cloth is placed on the table, and in following shots the things such as the cloth, bones and jewelry scattered on the table change position. (00:51:50)
Continuity mistake: When watching Will, Jack, and Norrington sword fight on the beach, Elizabeth's nose and cheeks are slightly sunburned. When back on the ship, they're only tanned, and no longer burned. (01:44:30 - 01:55:20)
Continuity mistake: After Jack takes the heart out of the chest he hurriedly closes its lid, the locks engage, and the key's end remains in the horizontal position when Jack runs off. However, when Pintel and Ragetti grab the chest the key's circular end is now vertical - the key does not turn itself. (01:51:00)
Continuity mistake: When Elizabeth questions Jack about his "broken" compass as they stand on deck, her left arm rests on the deck rail and changes position back and forth between shots. (01:36:30)
Continuity mistake: When Jack is trying to get the handcuff off his hand at the end of the movie, he has all of his rings turned inward to make it easier to get it off. But when the shot changes into a wide shot, as he pulls off the handcuffs, all of his rings are facing the right way. (02:09:10)
Continuity mistake: On the Pearl, after Elizabeth tells Norrington that she trusts Jack, when Norrington walks away from the deck rail, in the shots facing Elizabeth, the pretty cumulus clouds behind her change back and forth between shots. (01:28:50)
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.