Ariel signs Ursula's contract, with her name, showing that she knows how to write. However, when voiceless, she does not use this skill to write important information to Eric or anyone else who could help her.
At the end of the movie a rainbow is shown with the correct colors but with their order inverted.
When Ariel's voice is freed from the conch shell and floats over to her, she is barefoot. In the next full shot of her, she is wearing shoes.
During "Kiss the Girl", the fish swim up from a depth, but later, when Ariel and Eric fall out of the boat, they are shown in Ursula's ball standing in shallow water.
During the song "Les Poissons", Chef Louis sings "Then I pull out their bones" and he pulls out the fishes bones and the tail fins with them. Later on in the song he sings "Then you rub some salt in 'cause that makes it taste nice" as he rubs the salt on a fish tail with the tail fins still attached, although he already pulled the tail fins out.
As Ariel and Eric swim toward each other right before the enormous Ursula rises above the sea they exchange dialogue: "Eric, you've got to get away from here," "No, I won't leave you," but their lips never move.
In the "Kiss the Girl" sequence, when Ariel and Eric's reflections are shown in the water, Ariel's hair is in up in a ponytail, but when we see her in the boat, it is half up with a bow.
Just before Grimsby uncovers Eric's statue, the shirt of a sailor behind him changes color. (This was corrected in the 2006 Platinum Edition release.)
After Sebastian discovers Ariel's treasure cove and gets tangled up in her collection of human objects, he gets a thimble stuck on his claws. The thimble subsequently disappears and reappears between shots.
When Ursula is explaining the bargain to Ariel, she says that she will make Ariel a potion to turn her into a human. However, neither she nor Ariel drink any sort of potion; once she has Ariel's voice as payment, Ursula simply waves her arms and makes the transformation happen.
The statue is too big to fit in the hole to Ariel's cavern, but it somehow makes it in.
While in the castle of Prince Eric, Ariel lies down on a bed for the first time. Cut to Sebastian talking. Cut back to Ariel asleep on top of the covers. Next, Sebastian jumps on the bed, and Ariel is shown asleep under the covers.
When Ariel first enters her grotto she closes the door behind her, but when she swims out the door is already open.
During the song "Under the Sea" a flower in Ariel's hair disappears (after the yellow fish whirl around her) and reappears later.
When Eric and Ariel are reunited and she got her voice back on the ship, they are about to kiss but the sundown turns her into a mermaid again before they do. Ursula crawls towards them, catches Ariel, says "So long, loverboy" and jumps into the water. When they are seen in the next shot Ariel's blue dress is suddenly gone.
At the end of the "Kiss the Girl" scene, Ariel is slowly turning her head to the left to face Eric. During the motion between the 3/4 view of her face and the full side view, some animation frames are apparently missing and consequently the scene of Ariel moving her head is not smooth at all.
After Ariel and Flounder escape from the shark, Ariel has a bag over her shoulder, but when Ursula is watching from her cave the bag is gone.
When Ariel is singing "Part of Your World", she is lying on the sand, and when she gets up, her hair parts on the right side of her head. Then all of a sudden, it is parted on the left side.
The trim on Ariel's wedding dress changes from green to pink, then back to green and stays that color for the rest of the scene. (This was corrected in the 2006 Platinum Edition release.)
When Ariel is eating with Grimsby and Eric, her fork changes back and forth from three prongs to four prongs.
When Ariel sits down at the table and takes a fork, her nails are covered with pink varnish. Later no varnish is seen.
During the boat scene for the "Kiss the Girl" number, Eric can be seen using oars to row the boat. After he tries to guess Ariel's name, the oars disappear for the rest of the song.
When Eric is telling Grimsby that he wants to marry Vanessa, her hair is brown. When Vanessa is singing to herself in her cabin before the wedding and climbs onto the dresser, her hair turns black. Then at the wedding, it is brown again.
When Ariel and Flounder first talk to Scuttle, the pink shoulder bag disappears and reappears between shots.
When Ursula is on the boat right before her wedding to Eric she steps on the makeup table while she talks to herself in the mirror. In doing so she cracks a round crystal ball with her foot. But in the previous scene there was no such ball on the table.
When Ariel escapes through the porthole she does not have a bag on her shoulder. In the next shot she does.
When Ariel drops the bag to save Flounder from the shark, we do not see the bag until she picks it up off the floor.
When the crown falls off Triton's head it has eight prongs instead of usual five.
During the fireworks scene, the fireworks originate from the boat, but moments later, the boat has moved on but the fireworks are still erupting from the space where the boat had been.
When the Chef goes to poke Sebastian with the two-prong fork, the prongs trap Sebastian in between them and stick into the table. The holes that were supposed to be made by the fork were already there.
The eels Flotsam and Jetsam each have one yellow eye; one has it on the right side, the other on the left. When they are talking to Ariel and the camera cuts to the close-up of them saying "Together forever," the eyes have switched places.
When Triton remarks that the only problem that remains is how much he will miss Ariel, Sebastian looks up at him surprised. However, when he points his trident to Ariel to trade her fins for legs, Sebastian has disappeared. When Ariel sees she has been given legs and smiles broadly to her father, he is back.
When Prince Eric and Max the dog are first seen, the ship's balustrade that Max's paws are resting on is clearly visible through his paws.
When Sebastian looks through a pair of glasses, his right claw disappears for an instant.
When King Triton discovers Ariel's treasure cave, he destroys the statue of Eric. While it is breaking apart, a close up of the face shows cracks crawling across the entire face. However, later, when Flotsam and Jetsam are in the cave, they flick the face - now completely intact - to Ariel.
When Ariel sees a fork in a sunken ship for the first time, the fork has four tines. When Ariel takes it, it has only three.
While Ariel is singing "Part of Your World" on the rock, the sea is rough and choppy. But when we cut to the shot from behind, the sea is perfectly calm.
During the "Part of Your World" reprise, when Ariel is singing to Eric, she hears Max bark and looks to her left. But when Max runs into the frame, he approaches from what would have been her right.
Just as Scuttle starts leading the birds and sea creatures on the wedding crash, the guests, Eric, Vanessa, and the minister are not visible in the overhead shot as Scuttle and the birds begin diving toward them.
During the wedding scene, the shade of Vanessa's brown hair constantly changes back and forth from light to dark.
When Ursula is talking to Ariel for the first time, she sits down at her mirror to apply some makeup - when she looks at Ariel, she has on lipstick, but in the next shot, she has none and is applying it from a clam.
After Ariel becomes human the first time, Scuttle dresses her in a piece of sail cloth from the shipwreck. Moments later, Sebastian crawls into a pocket in the makeshift dress when there's no reason for a pocket to be sewn in a sail.
Throughout the part of the movie when Ariel has legs and is on land, Sebastian, Flounder and Scuttle all speak of how Ariel will regain her voice when Prince Eric has fallen in love with her and kissed her. However, when Ursula details the terms of the contract, it is never mentioned that Ariel's voice will be returned. If it was, then Ursula would have received no payment for giving Ariel legs.
When Sebastian is trying to escape from Louis the chef, he runs under a shelf of glassware, pots, and bowls. When we see Louis running towards the shelf, he is holding a butcher knife in his right hand. Then when we his reflection in one of the bowls in front of him, the butcher knife is reflected in the wrong hand (his left hand).
In the dinner scene with Ariel, Eric, and Grimsby, Sebastian crawls from Grimsby's plate to Ariel's at her signal, and the table is clean. At the end of the scene, little white footprints appear.
When Grimsby is talking to Eric at the dining table about taking Ariel out for a day on the town, there are plates in front of all of them. But when Carlotta brings the food they have no plates in front of them.
During "Les Poissons", while Sebastian is trying to sneak away under the lettuce, everything on the table disappears as Louis hits the fish with the mallet.
When Vanessa is singing while getting dressed for the wedding, she throws a spike to the mirror and the mirror bends. On the shot right before she steps on the bottle, the mirror is still, and on the next shot it is bent again and she is putting it still while revealing Ursula's face on the reflection.
During the final battle scene, where Ursula is about to strike Ariel with the trident, Eric steers the shipwreck into Ursula. The shot just before the ship pokes her, she is facing the wrong way (Ursula is facing Eric's direction when she should be facing Ariel).
The trident keeps on disappearing and reappearing in Ursula's hands without any time for her to pick it up whenever it is knocked out of her hands.
When Ursula is human and is singing in her chamber, she steps on the vanity where there was one purple jar to the right of the green box, but when she steps up, she smashes a new purple one that appears. When the shot zooms out, the smashed jar is now the only jar and is to the left of the green box.
In the opening sequence, Eric helps a sailor tighten a rope. The next shot is a close-up of Eric, where he is holding a much thinner, darker rope in his hand, which was nowhere to be seen earlier.
When the animals are sabotaging Eric's wedding to Vanessa, Scuttle tries to pull her seashell necklace away from her. The significance of the necklace should not be evident to him, as he wasn't there to see Ursula seal Ariel's voice inside it.
During a carriage ride, Ariel makes the carriage jump a small ravine. When it hits the other side, it stops briefly, and then begins to move. As it does, the wheels do not move at all, but remain motionless.
When Eric is waiting for Ariel to arrive at dinner, he doesn't cast a shadow.
When Max (Prince Eric's dog) sees Ariel for the first time, by the ship, he licks her right cheek, but when Max is called away Ariel dreamily feels her left cheek.
In the very beginning when King Triton comes to the hall for the celebration the chandelier is already lit but he lights it again.
During the dressing room scene with Ariel and her sisters, the sea flower she picks for her father does not appear until just after she looks at herself in the mirror.
When Ariel climbs onto the wedding ship she isn't wearing any shoes, but after the shell smashes and her voice returns she is.
During Kiss the Girl, Sebastian, Flounder and some of the fish cannot survive in fresh water as they are actually salt water fish.
In all the shots of Sebastian conducting the sea orchestra, his baton changes from a brown stick to an all-white baton, to finally a wooden baton with a black grip. If one pauses at the final shot of Sebastian during the concert, he drops his baton aside the moment he gasps when Ariel is absent.
In the 2013 Diamond Edition Blu-ray/DVD/Blu-ray3D/Digital HD release, the fade in the opening scene was mistimed. The opening credits were mistimed, and the "Silver Screen Partners IV" credit was missing in this release.
In the 2013 Diamond Edition Blu-ray/DVD/Blu-ray 3D/Digital HD release, the dissolve from "you really are a guppy" to Scuttle's first scene is cut short. This was later corrected and a disc exchange program was created to replace the Blu-ray/DVD discs.
In the 2013 Diamond Edition Blu-ray/DVD/Blu-ray3D/Digital HD release, the fade in the opening scene was mistimed. The opening credits were mistimed and the "Silver Screen Partners IV" credit was missing in this release.