Continuity mistake: Will comes into the blacksmith shop, comments about Mr. Brown and then approaches the anvil. In this shot the wood post on his right has a hammer and knotted rope hanging together on the same side. However, later when Jack sprays the soot at Will the same wood post is seen on Will's left and the rope hangs on another side of the post, not together with the hammer. That rope changes shape and position in other shots in between too. (00:22:15 - 00:26:15)
Continuity mistake: Anamaria has her hands on Jack's shoulders in the front shot, just as she said, "The Black Pearl is yours," and then she removes her hands. In the next successive side shot, her hands are still on Jack's shoulders, she then removes them again as she smiles at him. Jack's left sleeve is different in both shots. (02:12:15)
Continuity mistake: As the soldiers are firing at Jack after his escape, he runs across the footbridge. In the far wide shot, he crosses the center of the bridge and passes the man with the sack on his back. In the next close-up shot, Jack is just getting to the center of the bridge and starts to pass the man with the sack on his back. (00:20:20)
Continuity mistake: When Mr. Gibbs yells, "Load the guns! Case shot and langrage!" Will is behind him in this shot and Will's body is facing towards Anamaria, yet in Will's close-up, his body is facing towards Mr. Gibbs, and just then turns a bit, to face Anamaria and Elizabeth. (01:23:25)
Continuity mistake: When Jack hangs onto the beam and then in some close-ups while up on the beams, as he and Will are fighting, the large bandana around his head is soaked at his forehead. However, when he holds the gun on Will, the bandana is completely dry. (00:25:55)
Continuity mistake: Just before Will sends Jack up to the rafters, A close up of Jack's face shows a single hair going across his right eye. And then it's gone as he's sent up from close up. (00:25:50)
Continuity mistake: During the pirate attack on Port Royal, Will opens the door of the blacksmith shop, just as Jacoby runs past chasing a woman, and to Will's right, three men run up the stairs into the alcove as Will takes out his axe to start after Jacoby. In the very next wide shot of Will and the alcove, those three men aren't seen at all, but as soon as Will lifts the axe over his head to throw, one of those men from the previous shot is seen running up some stairs, past a shop. (00:31:10)
Continuity mistake: On the island, after regaining consciousness, when Jack puts his hands up to his face and desperately asks, "But why is the rum gone?" his fingernails are totally clean. However, in the earlier shots while getting drunk, his fingernails are very dirty, before passing out. (01:39:15)
Continuity mistake: Jack walks down to the dock where Interceptor's moored, Murtogg is sitting on a sack that lies on a crate, his feet are up on a small barrel and behind him to his left are two large barrels, one on top of another. Once Jack's confronted, now the two large barrels are closer to the beam, and the small barrel is up right against the crate. This has nothing to do with the angle of the camera. (00:11:40)
Continuity mistake: Jack chases after the monkey on the broken mast leading across to the Black Pearl. When he gets there, Barbossa says, "Why thank you, Jack." Barbossa's left arm is up and he's holding the rope. In that first shot, much of his white sleeve is out. In the next shot of Barbossa, the white sleeve is mostly covered. Then in his next shot, much of the white sleeve is out again. (01:29:50)
Continuity mistake: When skeletal Pintel and skeletal Ragetti are in the rowboat their appearance and parasols differ between shots, and later, when Pintel attacks Ragetti in the wide shot, the two oars are each hanging off its own side of the boat. However, in the close-up one oar is now lying across the two sides of the boat. (01:51:10)
Continuity mistake: When Jack and Elizabeth are on the island Jack lifts the hatch to the underground cache of rum. In the first shot from below, the top stair is visible at the opening above. In the next shot from above the design/shape of the top stair is very different. Bramble disappears between shots as well. (01:36:00)
Continuity mistake: When Elizabeth asks, "Well, then can't we lose them amongst those shoals?" in the front shot, her hair is in front of her shoulders and in the side shot, her hair is behind her shoulder, on her back. This occurs many times throughout the film with Elizabeth's loose, long hair - wet and dry, such as on the dock, after Jack rescues her in Port Royal, and after Will rescues her when they board the Interceptor. (01:21:40)
Continuity mistake: When Elizabeth and Jack are on the island drinking rum, the amount of rum in Jack's bottle changes between shots.
Continuity mistake: At the end when Norrington is talking to Will about it being a good sword, he holds the sword vertical. Camera cuts and it's now angled at Will. (02:07:00)
Continuity mistake: When Will is hanging from the mast while Jack is talking to him, the clouds in the background behind Jack changes more than normal during the shots. (00:48:00)
Continuity mistake: Murtogg and Mullroy rush over to help lift Elizabeth onto the pier. Murtogg drops his gun behind the two posts and Mullroy drops his gun in front of the two right corner posts. In the wide shot, Jack's holding the medallion and Norrington rushes in. Mullroy's gun isn't behind him, at the posts, and Murtogg's gun isn't positioned the same way he dropped it. When Norrington grabs Jack, Mullroy's gun is lying in front of the posts again. Also, the ropes' position changes in these shots too. (00:16:30)
Continuity mistake: When Governor Swann is leaning on the desk next to the drawer with the severed hand, his right hand is behind his back. In the close-up shot when he opens the drawer, his right hand is on his stomach, but in the wide shot his right hand is behind him again. (02:02:10)
Continuity mistake: Pintel yells out, "How do we tell?" and his jacket is covering a reasonable amount of the white shirt underneath. In the next shot of him when he's shot by Barbossa, more of the white shirt is visible, so the bullet hole can be seen. (01:12:50)
Continuity mistake: When the Black Pearl and the Interceptor fire their cannons, a fork's prongs dig into the iris of Ragetti's wooden eye. Pintel then removes the fork with the wooden eye, but the fork's prongs are now lodged just beside the iris of the eye - not to be confused with swirls in that eye; and his grip of the fork differs between shots. (01:25:30)
Answer: The curse needs the blood of everybody who took a coin from the chest. All the other pirates have already contributed so, as the movie opens, the only blood needed is Will's, substituting for his father. During the finale of the movie, Jack takes a coin from the chest, adding himself to the curse, so his blood is now required as well as Will's.
Tailkinker ★
But I didn't see any blood on the coins, and none of the pirates cut themselves, even before Will became part of the mix.
Yes, the other pirates did cut themselves before Will came into it, off-screen. The lack of blood on the coins can simply be explained as most of it dripping to the bottom of the chest, it being washed away by storms blown into the cave, or by the fact that they didn't drop that much blood on it in the first place.
When they had Elizabeth they believed she was Bill Turner's daughter, but they all thought the curse had failed, none of them had cut themselves so it makes zero sense.
They had been collecting back the coins for years. During that time they repaid their own blood. All they needed was the last coin and the blood of Bill Turner to break the spell.
lionhead