In an interview with the Australian magazine Cinema Papers in the early 1990s, the director, George Miller, revealed that the shoot had been extremely difficult as he was initially unfamiliar with Hollywood-style communication. In a meeting to discuss ways to reduce the budget Miller volunteered to give up his trailer because he was always needed on the set and had no time to use it. This was interpreted by the studio as him being a pushover, so they began to interfere with his production requests. If he asked for 50 extras, the studio would provide a dozen. If he asked for two cameras they would provide one. Miller decided to fight fire with fire and refused to shoot each scene until his production demands were met. The studio responded by looking for a new director but were prevented by Jack Nicholson, who supported Miller and vowed to walk off the production if he was replaced.
In 2008 John Updike wrote a sequel, "The Widows of Eastwick", to his 1984 "The Witches of Eastwick" novel. To date [August 2013] the film has neither been made nor been developed to be made.
A "grimoire" is a textbook of magic. The name of the one in the film was "Maleficio". Wikipedia states "such books typically include instructions on how to create magical objects like talismans and amulets, how to perform magical spells, charms and divination and also how to summon or invoke supernatural entities such as angels, spirits, and demons".
When Darrel is driving the car back to the house to confront the girls, the car crashes, losing the rear licenses plate. When he arrives home, the plate is back on the car.
When Jane is practicing her cello at home and a string breaks, in the next short clip showing her head all four strings are still intact. Later, when Daryl makes her play, the broken string is fixed - they couldn't have replaced it in between as the scene is continuous.