गूफ़

The length of Nancy's fingernails changes repeatedly during the sex ritual - they're noticeably longer in shots where Sandra Dee's face is visible, implying that a body double with shorter nails was used for the racier portions of the scene.

Every person in the movie pronounces the town's name as "Dun-witch"; in fact, it is pronounced "Dun-itch", with a silent W. Though to be fair, it's not uncommon for U.S. cities named for those in other countries to be given American pronunciations (e.g., Cairo, IL, is pronounced "KAY-ro," not "KYE-ro").