Continuity mistake: When William is talking to Cutler Beckett after being arrested, a fishing ship is seen out on the ocean, not moving. In the next shot, the ship has disappeared. (00:10:20)
Continuity mistake: In the scene where the crew of the Black Pearl is in the two cages climbing up the ravine wall on vines, in one shot, the smaller cage is significantly further behind the one with Will, Gibbs and the others. In the next shot, when there is the conversation about, "it would only take about six," to crew the Pearl, the smaller cage is even with the larger one. (00:35:50)
Continuity mistake: This occurs during and after the scene where Jack empties the sand out of the jar and puts the heart inside. After replacing most of the sand, in the later shots the amount of sand in the jar keeps changing. Later in the scene on the Black Pearl, the amount of sand changes from shot-to-shot up until the jar is dropped and breaks. (01:51:40)
Continuity mistake: In the scene where the two sailors have found Jack's hat in the water, they try it on in turn. When the second man tried it on, the hat changes position between shots, with no time for him to move it. In one shot, one of the corners is facing front, in the next shot a flat side is facing the front. (00:17:50)
Continuity mistake: When trying to flee, Norrington falls and drops his sword and the chest. As he crawls in the first shot, note the sword's hilt and particularly the hand guard, with its wide part facing up. In the next shot the direction of the hand guard has changed, with its wide part now facing the ground (this has nothing to do with camera angle). (01:58:45)
Continuity mistake: When Pintel and Ragetti argue over the pronunciation of "Kraken" while they're rowing, the loose end of Jack's red bandanna changes position and jumps from his back to over his shoulder, between shots more than once. (01:38:30)
Continuity mistake: When Captain Bellamy and his sailors stand on deck, looking at the flaming Tortuga, their positions differ between the shot facing them and the next shot, from behind. (01:07:10)
Continuity mistake: When Jack, Elizabeth and Norrington remove the small chest from the larger one, and when Will kneels beside them, there are letters, etc lying on the large chest's lid, which change, disappear and reappear. (01:41:20)
Continuity mistake: When the cannibal women throw fruit at Jack, the large papaya hits the pole's point and the end of the fruit actually smashes. However, in the next shot it slides across the pole with a perfect circular hole. (00:41:05)
Continuity mistake: Aboard the Flying Dutchman, when Will sneaks in to steal the key, as the shot draws closer to Jones the quills are shown on the organ keys - with one leaning over the keys. In the next shot, as Will reaches sleeping Jones, both quills are leaning away from the keys, and an extra quill stick (feather free) suddenly appears. (01:24:00)
Continuity mistake: After Jack has escaped from the island where he was going to be burned, the makeup on his face (the eyes) changes between scenes. The makeup has faded quite considerably when he first boards the Black Pearl then in a later scene the makeup is neater and clearer. (00:42:30)
Continuity mistake: After Jack explains the legend of Davy Jones to Elizabeth, and they have found their heading, Elizabeth's braid is going down her back. When Jack points Elizabeth toward the ship her braid is now on her right shoulder. She doesn't move her head and there is not enough time for her to move it herself. (01:17:00)
Revealing mistake: On the beach during the sword fight after the chest is found, in one overhead shot it shows the three men are casting shadows in different directions, revealing the presence of on-set lighting. (01:43:50)
Continuity mistake: When Jack "intuitively" inquires about Elizabeth's feelings, the dangling beads in his hair are over his dreadlocks, near his shoulder. Next close-up they're tucked under his hair. This type of thing - with all the do-dads in Jack's hair - occurs numerous times throughout the film. (01:35:20)
Continuity mistake: After arresting Will and Elizabeth, when Cutler Beckett holds up Norrington's arrest note, the way the paper is folded and how he holds it differs between shots. (00:03:20)
Continuity mistake: After the ship with the "bride spirit" is attacked by the Kraken, Will ends up underwater, and when he surfaces his hair is soaked and slicked back, as he climbs on the ship's debris. However, in the next shot, his hair is parted, stringy and falling to the front. (01:33:50)
Continuity mistake: While Elizabeth listens as Captain Bellamy tells his crew that the stowaway is likely naked, she drops the paint brush into the pail. When it cuts to the close-up, the paint brush handle rests much higher in the pail. (00:46:05)
Continuity mistake: The actual position of the burning word "Tortuga" differs between the first shot as it begins to burn on deck and from the close-up of the flames. (01:04:15)
Continuity mistake: After Bootstrap gives Jack the black mark, when Gibbs shouts, "Back to your stations, the lot o'ya," the cloth round his neck changes position, depending on camera angle. (00:17:00)
Continuity mistake: Aboard the Pearl, when Elizabeth reaches for the gun at the top of the stairs, her hand is clean as Jack appears. As she hugs Jack's leg, her hand/fingernails are black and filthy. (02:04:10)
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.