Corrected entry: Later on in the movie after the scientists place Madison in the "fish tank", she stays there for a while until Allen comes to visit her. When he runs up to the tank, and she swims up to the surface, watch all of her fin. Now think, people...would a fish bend his body as if he had knees underneath? It looks as if Madison had knees underneath her fin, since it's bending in that sort of manner.
Grumpy Scot
8th Oct 2002
Correction: If we assume Mermaids are a divergent human evolution, then the bones in her tail might be more like two legs fused together instead of a structure more similar to a real fish. She might very well have a joint there.
Grumpy Scot