Continuity mistake: When Lord Beckett is trying to convince Will Turner to go after Jack Sparrow, he picks up a red hot poker from the fire and says that they've marked each other. The shot cuts to Will who asks simply "How did he mark you?" at which point the shot cuts back to Beckett and the formerly red-hot poker is already now a much cooler black. Glowing hot iron does not cool that quickly in air. (00:09:30)
Factual error: The formal title of the East India Trading Company is the Honourable East India Company or HEIC; official merchandise provided by said company would not be affixed merely with the letters EIC but rather HEIC.
Other mistake: Whilst the crew are escaping Pelegosto, Jack climbs onto the boat and he is hit by a wave and he gets soaking wet. But if you look before he gets hit by the wave, you can see his clothes are already soaking wet, and his chief make-up has washed off before the wave hits him. (00:42:20)
Revealing mistake: When Jack, Elizabeth, Norrington and the crew are sailing to meet the Dutchmen, you can see the water is moving past the Pearl, showing the Pearl in motion on the water. There is then one shot of Elizabeth and the sea behind her is completely still and not moving past the Pearl. Camera cuts and again the sea is moving past the Pearl.
Continuity mistake: When Elizabeth sits in the rain, holding her bouquet of wedding flowers, many long hair strands hang down her forehead. However, when she runs to Will there are far less loose strands of hair, and the hair pulled back is neater. (00:01:25)
Continuity mistake: When the cannibal women place the necklace of many fingers and toes around Jack's neck, the digits of multi-skin color and size are tied and hang in a specific way. When Jack seasons himself with paprika, the digits are different. (00:32:05)
Continuity mistake: When Jack spills oil on his cuffed hand, his fingers and nails are filthy as he slips the shackle off. However, next shot, when his hand is free, his nails are not nearly as black. (02:13:40)
Audio problem: When Will sneaks into Davy Jones' chamber and tries to take the key from him, as Davy Jones' tentacles slip and hit the notes on his organ, they only fall on one or two notes, but we hear a full minor chord (which would require three notes at equal length from each to be played). (01:24:30)
Continuity mistake: Tia Dalma gives Jack a jar of dirt (brown, clotty-ish), but later in the movie, it is sand. (00:53:10 - 01:57:30)
Continuity mistake: While Elizabeth hides, Beckett walks into his office and the wood chest is in the foreground; under the lid the paper sticks out, with an edge that is creased and has writing. When Beckett lifts the lid the crease is gone and the writing differs. (00:26:50)
Revealing mistake: Elizabeth says."Oh the heat." You can see the exact spot where she is going to fake faint, from previous takes. (01:44:35)
Continuity mistake: In the scene where Jack meets Bootstrap, Bootstrap's hands are filled with barnacles but when he touches Jack's hand to give him "the black spot" his hand is suddenly blue with no barnacles. (00:13:50 - 00:15:30)
Continuity mistake: When Jack, Will and Norrington fight for the key, Elizabeth tries to stop them by "fainting". After she gets up after her plan has failed, Pintel and Ragetti are seen running past Elizabeth in the background with the chest. In the next shot, they run past Elizabeth again. (01:44:30)
Continuity mistake: When captain Jack Sparrow gets slimed by the Kraken, Jack's hat lands on deck, slime-free. In the next shot, the hat is in a glob of slime. (02:09:30)
Continuity mistake: When the two women put the necklace around Jack's neck they are stood next to each other and are close enough that they are touching each other as they put the necklace on. When the shot changes they are stood around 1ft away from each other. (00:31:20)
Continuity mistake: When Jack first gets slimed, in the shot of him to the side there is a glob of slime on his chest dripping to the floor. When the shot changes to in front of Jack, this glob of slime has gone and is replaced a second later. (02:09:20)
Continuity mistake: Beckett tells Elizabeth that she needs to up her offer. She replies by cocking the gun that is under Beckett's chin. Beckett then walks with the gun under his chin to his desk. However, when he arrives at his desk, the gun is now by his right cheek. (00:28:50)
Continuity mistake: When talking to Bootstrap for the first time, Bootstrap is saying how he was thinking about any chance of escape he would take it. When he's talking, the bone in Jack's hair switches from uncovered to covered between the long and close shots. (00:15:10)
Continuity mistake: When Jack, Norrington and Elizabeth find the chest, the amount of flowers visible changes instantly. (01:41:20)
Continuity mistake: When Norrington, Elizabeth and Jack find the chest they wipe some sand off and there are black parts of the chest visible. When they pull the chest out of the ground, all the black bits are gone and is covered in sand.
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.