Visible crew/equipment: Towards the end, as Vicomte de Valmont is demanding a simple yes or no, there's a shot of Marquise de Merteuil in front of a mirror, slowly panning back. Just after he says "yes or no," we see a shadow/silhouette in the mirror moving, but Valmont is standing perfectly still, and no one else is in the room.
Dangerous Liaisons (1988)
1 visible crew/equipment mistake - chronological order
Directed by: Stephen Frears
Starring: Keanu Reeves, Michelle Pfeiffer, John Malkovich, Glenn Close, Uma Thurman, Swoosie Kurtz
Continuity mistake: When Valmont is waving the letter behind his back, in the closeup the address is facing upwards, but in the wider shot we can see the wax seal is now visible.
Vicomte de Valmont: Why do you suppose we only feel compelled to chase the ones who run away?
Marquise de Merteuil: Immaturity?
More questions & answers from Dangerous Liaisons
Chosen answer: It looked to me like they were performing what is known as "cupping". "Cupping" is a branch of Chinese medicine where a cup (often heated, the so-called "fire cupping") is used to create a vacuum on certain areas of the skin, to simulate acupressure. It is said to relieve respiratory problems and muscular pains ad to stimulate the flow of life energy in the patient. How these French nuns came to know of and approve of the technique is another matter..
Twotall