The fullness of the invisibility spray bottle varies widely during several scenes.
Dexter Riley's vision is corrected by an invisible eyeglass lens. That should not have been possible because eyeglasses correct vision by refracting light.
Dexter indicates to Dean Higgins that he's read a book on Quantum Mechanics by fictional 18th century Russian scientist Bersakov. While scientific inquiry into the wave nature of light began in the 17th and 18th centuries with Hooke, Huygens, and Euler, the earliest work in modern quantum mechanics didn't occur until Max Planck's quantum hypothesis in 1900 at least 100 years after Bersakov may have lived.
It is a violation of PGA regulations to offer a competitor advice during play. When Dean Higgins offered pointers to Billy Casper at the tee, officials should have assessed Higgins a penalty.
When chasing the invisible car, Dexter tells the other college students to keep their eye or for anything. Just after that the invisible cast drives through a puddle of water on the side of the road without having any effect on the tires becoming visible again. This should have happened since water is what neutralizes the invisibly spray.
When Dexter, Kurt Russell, dips things in the invisibility solution like the tweezers and the ruler you can see for an instant the end that falls off so as to give the appearance of invisibility.
When Dexter taps his glasses on the edge of the bowl containing the invisibility solution there are no ripples in the solution only the sound to let us know that he is tapping the bowl.
When Schuyler was sprayed with the phony invisibility spray, he proceeded with a demonstration of its effects long after he should have noticed his hands had not been made invisible.
Druffle wrote a note to the effect that he had been "bitten" by a bumblebee. Bumblebees don't bite; they sting.