Two thoughts (spoilers)

My DVD says that the ending was something Hitchcock would have loved. During the 1980's I saw an 'Alfred Hitchcock presents' drama* in which a woman bribes the grave digger in a woman's prison to help her escape. When he has to bury the next victim she will sneak in the coffin besides the victim, he will bury them and then return later to let her out and make good her escape. Well the plan seems to work until the woman realises, too late, that she's been buried with the grave digger who is the next death! So perhaps this was inspired by Spoorlos?

(* These dramas were not written or directed by Hitch, just ones he gave his name to as they were in keeping with his legend.)

The creepiest scene in the film, and one that foreshadows the outcome, was when Rex and Saskia's car breaks down in the tunnel and he leaves her there to go and fetch petrol. When he returns she has disappeared from the car and when they are reunited he promises never to abandon her again. Very poignant given the film's denoument.

I'm a fountain of blood
In the shape of a girl