When the cars are approaching the cliff, a wide-angle shot shows they are driving on dirt. But in the close-ups (from the driver's view) they are driving on a highway with road stripes.
--------- When the road appears as a dirt road, that is the viewer seeing where the car is really driving. When the road is seen is from the driver's point of view and the car appear to be driving on a proper road with road markings, this is what the driver THINKS he is seeing, due to the witch's spell.
The witch is sitting in the back of Helen's car in one shot but from the view of the outside of the car the back seat is empty.
In Grandma's bedroom, just before the witch appears, the camera is panning slowly. One of the studio lights is visible in a reflection on the glass covering of a photo on the bedside table for a moment.
Although Inspector Baldwin makes a point of showing the Laniers the Devil Doll found at Myles Forrester's office after his death, he later makes no mention of the Devil Doll tied to Helen Lanier's car after her crash despite telling Bill Lanier that he had examined the scene thoroughly.
Bill and Todd Lanier do not have a Devil Doll tied to their car when they are bewitched and almost go over the quarry cliff, even though the charm was necessary for sending Helen Lanier over the same cliff and was also needed to cause the death of Myles Forrester.
Bill and Todd tell Tracy that May Eve is the witch's sabbat called "Roodmas", then proceed to name "the four great sabbats" as Candlemas, Roodmas, "Beltane in midsummer", and Halloween. Roodmas is actually the Christian Feast of the Cross, it's celebrated on May 3 or September 14, and has nothing to do with witches. Beltane is the actual May Eve sabbat, and doesn't happen in midsummer (that would be Litha, which is not one of the four great sabbats). Candlemas and Halloween are correct, but in reference to witches' religious customs, they should be more appropriately called Imbolc and Samhain, respectively. Lughnasadh is the missing fourth sabbat.
Although Lon Chaney, Jr. portrays a member of the Whitlocks, a prominent local English family, he speaks in a pronounced American accent throughout the film.