Corrected entry: After Norman flips off the boater, Ethel does the same. He yells at her for doing so and she replies that it was OK because he did it. However, she did not see him do it, because her back was to him.
Corrected entry: When Norman and Ethel are purchasing fuel for their boat, the total price on the fuel pump reads $19.00. As the boys watch Norman and Ethel leaving the dock the total price on the pump now reads $1.32. (Point of interest: as gasoline prices were increasing rapidly in the U.S. in the 1980's some of the older mechanical fuel pumps had a limit on the price per gallon so it was not uncommon for them to be set at half price and the totals had to be doubled ($38 instead of $19) until the pumps could be re-fitted). (00:13:00 - 00:14:25)
Correction: The price you see as the boys watch them leave is on the opposite side of the pump of Norman's $19 price. Not a movie mistake.
Correction: He sticks his hand, middle finger extended, out way over Ethel's head, such that it's visible to her.