older movie blue dots please help me out?

The Mephisto Waltz (1971)

IMDb synopsis:

Myles Clarkson is a journalist who was a classical piano player once on the rise. He interviews and is befriended by famed pianist Duncan Ely (Curt Jurgens), who is terminally ill. Unknown to Myles, Ely is a satanist who plans to have their souls switch places at his death so that he can be young again and continue to be an artist. Meddling in his plans is Myles' wife, Paula (Jacqueline Bisset), who is supicious of Ely and his too-familiar daughter, Roxanne (Barbara Parkins).

Also in the cast are Bradford Dillman, Pamelyn (Pamela) Ferdin, Kathleen Widdoes and William Windom.

Here are clips from the movie:

http://www.youtube.com/watch?v=zl0Rd2klaTI

http://www.youtube.com/watch?v=m6I5mLhyhfg

I've long been convinced that the dog wearing the human mask inspired the dog with a man's head in the remake of "Invasion of the Body Snatchers" (1978).

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Over the years, I have watched this one countless times and have read Fred Mustard Stewart's novel several times. Something about it has always bothered me deeply, but I've never had it answered though the story seems fairly straightforward.