Splash is a really well-made Hollywood fantasy comedy, with early Tom Hanks already developing into the charismatic everyman and Darryl Hannah and John Candy at their best. But under the comedy and sweetness I have always thought there was a disturbing undertone of extreme pessimism--just what kind of ugly and cruel society do we live in, in which the mermaid Madison's only prospect is that she will be tortured, from which Hanks' character ultimately has to flee, never to see his beloved brother again? (The same dark undertone is even more pronounced, I think, in Ron Howard's next big hit Cocoon, where the old folks willingly escape an earth and families that don't seem to offer them anything anymore.)
