Despite all the signs for the family-owned gas stations saying "Heyward", at the end of the movie when the real Scott shows Diane his driver's license, the last name is spelled "Hayward".
In the closeups the carburetors on the "Rawhide" boat have vertical velocity stacks, while during the race, in the long shots, the carbs have horizontal scoops angled off to the side.
The registration number of Elvis' ski boat (FL 1128 AE) changes between the wide and the close-up shots.
During the "Who Needs Money" song, the ships in the background are first pointed to the right, and in the next shot are pointed to the left.
In Scott and Dianne's first ski scene together, the stunt double for Shelley Fabares has hair that is less than a third as long.
As Scott drives along the highway at the end of the movie, he reveals his true identity and shows his driver license. As he shows evidence of his true name, his eyes are listed as brown (brn) when they are bright blue.
At the beginning of the movie Elvis is driving a red convertible and entering Florida. The sign says "Welcome to Florida, the Happy State". Florida is the Sunshine State.
The small sailboat in the boat shop has a registration of CF 0258 ML
which is a California registration number. Florida has had a 30-day registration period for boats from out-of-state for many years and Florida vessels have an FL identifier.
In the campfire scene, Scott takes out his guitar and proceeds to serenade Dianne. A combo of instruments kicks in, but no guitar sounds are present anywhere.
Elvis plays an electric guitar during the song "Clambake", but it is not plugged into an amp.
Just before Scott punches James near the end of the film in the hotel, Scott's hair bangs are parted, then one instant later they are very solid.
Diane's feet are dirty in the first water ski sequence.
At the end of the movie, Scott's operator's license does not list a town or city for his address, just a street and Texas. It also says he is 6 feet 2 inches tall. Elvis was just 6 feet tall.
When Sam Burton is talking to Scott next to the damaged boat, he said "I always missed NOT having a son", which implies he has a son and is not happy about it. He likely meant to say "regretted" instead of "missed" or "I always missed having a son".
While Scott is driving in Miami, mountains are visible in the background.
While Scott (who had been pretending to be Tom) and Dianne are driving in Miami at the end of the movie, Scott points to an oil field full of operating oil wells. There are no oil wells in Miami .
Several evening scenes show the sun setting over the water. This would not happen in Miami, which is on the East Coast.
During the boat race, there is a little boy sitting right behind Mr. Hayward who is pretending (not very well) to eat a hot dog.