Continuity mistake: When Angelica is about to tell Jack that she loves him, his position alternates back and forth between being perpendicular to her a meter away, to face to face at half a meter distance.
Continuity mistake: When Jack has each foot on a different carriage, the left side driver's whip extends to the right carriage, yet disappears a frame later.
Continuity mistake: When Angelica and Jack are drinking and talking about the past, the hair bang on her forehead swaps between loose and tucked under the bandana.
Continuity mistake: When Jack is rowing the boat towards the island, Angelica's hair falls over her back, with a mere strand falling over her left shoulder. When the angle changes, all of her hair is now over her left shoulder.
Continuity mistake: Jack strands Angelica on an island and tosses a gun on the floor. The gun swaps from laying on an 11 o'clock direction, to a 1 o'clock between shots.
Continuity mistake: When the mermaid is by the tree, the left part of the shirt's collar keeps changing positions, appearing and disappearing between shots.
Continuity mistake: Philip carries the mermaid to the tree's root, kneels down and then stands up. When the angle changes he is in the process of standing up again.
Continuity mistake: After Philip opens the water tank, the mermaid raises her head reaching for air, and takes her right arm towards the edge of the tank. A frame later the arm is down, under the water.
Continuity mistake: Jack is on top of the carriage's roof, passes by a group of columns and then by two arched buildings. When the angle changes to a ground level of the carriage, it's still passing by the previous columns.
Continuity mistake: After the mermaid stands up aided by Philip, the weeds between her knees disappears between shots.
Continuity mistake: When Blackbeard shows up and hangs Jack upside down, Jack falls on the floor with his hair messed up. As of then, his hairstyle changes between shots despite him not moving.
Other mistake: In the mutiny scene where the cook is torched, the distance between the long boat and the Queen Anne's Revenge increases when the cook is only shown paddling away after the QAR turns towards it.
Continuity mistake: During the fight for the chalices, wounded Philip walks towards the mermaid, who is tied around a tree. Her right arm is straight, yet a frame later it's bent.
Chosen answer: She most likely went to stop the ritual, she probably didn't want her tear to be used by the likes of Blackbeard. She knew that Jack would use it wisely.