When Madison must go back to the ocean, she tells Allen that he can go with her, but he will never be able to return to land. It is never explained why, perhaps it may have to do with the sea hag subplot. Still, he was reluctant at first but accepts readily after saving her from government frogmen. It's somewhat a Bittersweet Ending; the bitter part is Allen will never see his brother, friends, or even Kornbluth again. The sweet part is being with Madison always. So, the question is, why couldn't he return?
- It's explained in the sequel, as Madison reveals that she was just kidding and that it's actually perfectly okay for them to go back to land, so it's possible it was a test question, how much would a human be willing to give up for his aquatic lover? Once Madison realized Allen was really going to stay with her, it was safe to tell him the truth.
- Seems like it. YMMV, but Pirates of the Caribbean: On Stranger Tides seems to contain several Shout Outs to Splash, such as mermaids turning human when dry, and back to mermaid when wet. It is explained in the movie that a mermaid's kiss prevents drowning. It is implied to be the same in Splash.
- The same thing happens in Hook, when Peter falls into the sea and mermaids rescue him and prevent him from drowning via kisses. Is it possible this is connected to mermaid folk stories?
- Why is Ross, who orders Madison's dissection is so keen on this when he could go down in history as the one who, (After an unfortunate misunderstanding,) established contact with a new race? Anything gained on the operating table is utterly crushed by the gravy-train of talk-show appearances, Nobel prizes, new history books and other awards piled on top of him.
- Maybe Ross is a sick sadist who just wants to vivisect a person and then hide under the excuse that she was not human.