Continuity mistake: When Triton is turned into a seaweed, the crown has prongs all around it. When Ursula picks it up, the number of prongs has disappeared and the crown is now a diadem.
Continuity mistake: The cake where Ursula comes out-of disappears from the boat's deck between shots.
Continuity mistake: Before Eric is given his statue he sits on a barrel. After he stands up and walks towards the statue the barrel disappears.
Continuity mistake: The right side of the rock where Sebastian places the music sheet is noticeably raised to allow for him to place it there, but swaps to flat in the wide angle.
Continuity mistake: The first time we see Eric's ship the lanterns have a quadrant pattern. In the following shots they swap to three parallel lines.
Continuity mistake: When Grimsby walks Eric away from the beach, and Ariel sings, the rock where she stands changes from a slim pointy rock, to a squared bulky block between shots.
Continuity mistake: When the storm breaks, in the wide angle showing how a lightning lights the side of the ship, Ariel and Scuttle have disappeared, only to reappear in the following close-up.
Continuity mistake: On the boat, Eric steps by the window where Ariel is peeping, yet when the angle changes he is several meters to the left, where the rope ladder is.
Continuity mistake: While human-Ariel is showing her dress, Eric's dog comes running, Flounder panics and dives in. Thing is, the scenery keeps changing in every single angle.
Continuity mistake: When Ariel takes Flounder out of the porthole, a broken log forming a big crack suddenly appears above him.
Continuity mistake: When Eric's dog comes running on the beach and scares Ariel, Flounder, Scuttle, and Sebastian, all the stuff around them (logs, barrels, iron parts) disappears.
Continuity mistake: When Scuttle examines the fork, Ariel's bag suddenly disappears, only to reappear when he blows the pipe.
Continuity mistake: When Flounder gets trapped in the porthole, from the angle outside there are two wooden beams 20 cm away from each side. From inside the ship, the distance has increased to a meter.
Continuity mistake: When the film starts, Ariel sets eyes on a sunken ship with a basement access on the deck, and a broken and skewed door on it. When she swims towards the boat, basement and door are gone.
Continuity mistake: The mast onto which Ariel rests when the film starts, shrinks to a third of its size in the close-ups, plus a rope suddenly appears in front of it.
Continuity mistake: In the chef's kitchen, there's a big recipe book. Its page marker changes styles when Louis is about to chop the fish.
Continuity mistake: A brown pear appears in the fruit bowl on the dinner table.
Continuity mistake: During dinner, the fork that Ariel is about to grab swaps from having a round bottom part, to crafted petals.
Continuity mistake: When Ariel makes her dress with a sail and ropes, it looks really poor, with the ropes surrounding her body. When she climbs on the rock, the dress looks perfect, and the ropes are neatly aligned on the top part and waist.
Chosen answer: They are all throughout the film but the biggest one is when Eric is steering the ship to stab or skewer Ursula.
Disney-Freak