Revealing mistake: When the car Paul is driving spins out of control and flips, the roll bar is visible through the back window.
Revealing mistake: Look closely during Clive's argument with Graeme. You can see Ruth's left eye which is supposedly blind, actually appear normal behind her glasses' dark lens.
Chosen answer: The movie "Paul" was riddled with inside jokes and homages to classic science fiction and adventure movies and tv shows, so it would not be surprising there would be a reference from an Indiana Jones movie. Also, Paul is, indeed, "short" with a "round" head.
Scott215