Directed by: Ron Howard
Starring: Daryl Hannah, Eugene Levy, John Candy, Tom Hanks
Revealing mistake: When Hanks drives through the city escaping form the MPs, the guy driving is a very obvious stuntman.
Sacha
Continuity mistake: Allen drives through a spotless park, but, when the angle cuts, a flock of pigeons appears ahead.
Sacha 
Continuity mistake: When Tom Hanks is in the dinghy by himself, the outboard motor has no cover. He falls into the water and the dinghy circles him several times. One of the shots shows the motor with its cover in place. (It is an Evinrude motor).
Walter Kornbluth: I was right! Behold the mermaid.
Trivia: The man in charge of the ice skate rentals who tackles Allen when he tries to run out with his skates still on is the film's screenwriter Babaloo Mandel.
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Answer: The sea hag gives Madison a set of instructions she has to carry out, and tells her that she can only survive out of the ocean for six days. She also tells her she has to wet her tail every day, which is why Madison is seen in the bathtub.
raywestThat's why she took a bath that night and got her legs wet turning them into fins.