When Flounder tries to explain why he and Ariel missed the concert to King Triton, his face turns into Scuttle while he talks about the seagull, and turns into a shark when he talks about the shark.
When Ariel goes to her grotto, she moves a heavy rock to get in, and it closes right behind her. Sebastian even has to squeeze to get through. But when she leaves, the rock has been pushed out to the side.
On the ship, as Eric is receiving his birthday present, one of the sailors' shirts changes suddenly from white to blue.
In the scene where Vanessa is getting ready for the wedding, she steps on a red container when she climbs onto the dresser. The container isn't there one second, and appears for her to step on.
When the shell holding Ariel's voice breaks, at first she is barefoot, and then she appears to be wearing shoes.
One of the most famous "mistakes" is the wedding scene, where the priest appears to be "excited". Some argue that it is his knee.
