When Lamont disables Miss Ferris' car he slams the hood but it doesn't close. It can be seen gaping open while he is inside the car accessing the glove box. He walks away and the hood is not closed. Later, When the car won't start Lamont has Miss Ferris open the hood so he can check out the issue.
When Perry and Della are driving to check Madge's car and garage for evidence Della misstates her name as Marge in her first question to Perry. "Why wouldn't Marge have told us about going out there?"
When Lamont is giving Arlene Ferris a ride, after disabling her car, there is a shadow of a hand in the corner of the back seat, behind Arlene. Update: Arlene Ferris' hair is arranged in a popular hairdo at the time called a 'flip'. The shadow on the rear support (between the rear windshield and the passenger side window) is caused by the flipped up portion of her hairdo. Note that, as she turns her head to look at Lamont then back to look out the front, the shadow makes corresponding moves.
Loring Jr.'s beach house and surrounding area is clearly an indoor sound stage set that includes both ocean sound effects and Joshua trees. Joshua trees are desert trees, they do not grow by the ocean. Joshua trees grow far inland in SE California, southern Nevada, and Arizona.
The end credits list the Benson Fong character as "Colong Kim" instead of "Oolong Kim" which messes up the "O.K." initials plot line.