

Continuity mistake: When Grimsby is presenting the statue of Eric to the prince, one of the crew's shirts changes colour from white/black stripes to blue/black stripes.
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Continuity mistake: When Ariel is in the Prince's guest bedroom, the covers suddenly appear over her.
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Continuity mistake: The first time Ariel sees a fork it has 4 prongs. When she grabs it has 3.
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Sacha

Continuity mistake: When Ariel is crying and Sebastian comes to comfort her, there's a vase, two planks and a small bottle behind her. When the angle changes, every object is different, even the area looks much wider.
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Sacha

Continuity mistake: During the "Kiss the Girl" song a bunch of fish swim up underneath the boat, and the water is seen to be very deep. After the boat is knocked over however, Ariel and Eric are standing in the water which now appears to be only a few feet deep.
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Krista
Continuity mistake: When Sebastian is in Ariel's cavern with all her treasures, he accidentally gets his legs caught in a thimble. You can see it from the front, but when they show a shot from the back, it is gone. In the following shot from the front, it is back on again.
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Continuity mistake: When Ariel and Eric are in the boat together before their attempt to kiss, Ariel's hair is down. But in their shadows on the water, her hair is in a ponytail.
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Krista
Continuity mistake: At the table with Ariel and Eric, the stuff on Grimsby's dish changes positions in every single angle, and even disappears in the final angle.
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Sacha

Continuity mistake: After becoming human, Ariel swims and rest on a floating rock amidst the sea. A frame later she is laying on a rocky wall by the shore.
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Sacha

Continuity mistake: When we first meet Max, his front paws swap from white in the front angle, to grey in the angle shot from behind.
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Sacha

Revealing mistake: When we first see Max, his paws are leaning on a balustrade and become transparent. Though it may seem like it's an optical effect because they're in the shadows, the next angle shows them fully lit and opaque.
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Sacha

Continuity mistake: When Ariel spies the guys on the boat, she is under an arched window. Depending on the angle, the space is made of 3 blocks of wood, or 2. This keeps changing randomly all the time.
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Sacha

Continuity mistake: The bowl in which the chef dips Sebastian swaps from grey coloured to blue.
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Sacha

Continuity mistake: The lettuce under which Sebastian later hides, wasn't on the table in the first place.
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Sacha

Continuity mistake: During the eels scene, when Ariel is crying, the stone she lays on is a single stone laying almost flat on the sand; then swaps to a double stone, and when she sends the eels away it is a single stone though way steeper, standing upright.
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Sacha

Continuity mistake: When Grimsby is presenting the statue of Eric, the huge ribbon around it disappears between shots.
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Sacha

Continuity mistake: Eric's statue changes between shots, notice the position of the right fist.
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Sacha

Trivia: The King and Grand Duke from Cinderella (1950) appear in a brief cameo while attending the attempted royal wedding of Prince Eric and Vanessa, and can be seen when Max runs past the guests just before he bites Vanessa.
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Super Grover