Trivia: The original ending had Ernest still alive at old age, having lived a full life with his wife. When they are having a picnic in a park in beautiful Switzerland, Madeline and Helen are there also. They still look perfect, having coffee on a balcony of a hotel, but are bored to death. The movie ended with Ernest holding his wife's old hand with his still young hand. As the movie faded to black, the beautiful faces of Mad and Hel turned to skulls for a moment, giving us a last eerie look at the women.
Trivia: In the movie trailer only, Madeline parks her Mercedes behind a DeLorean, the car from Back to the Future, also a Robert Zemeckis film.
Trivia: When Madeleine is in the morgue, we get a shot of a table and on that table is a jar with a brain and formaldehyde in it, and on the jar is a sign and the sign says "abnormal." This is a homage to the film "Young Frankenstein": Dr Frankenstein sent Igor to the morgue to get a specific brain, an intelligent man's brain, but Igor was startled and dropped the intelligent brain, so looked around for another one and he did: He found a brain with the label "abnormal" on it, and that is why the monster was so hard to teach and control.
Chosen answer: CGI, just like any other difficult effect.
Grumpy Scot