starliteyes

Just off the top of my head - Robert Wagner in With a Song in My Heart?

Casablanca An experiment gone awry

Nanette Fabray was in The Private Lives of Elizabeth and Essex with Errol Flynn.

Clooney, Rosemary

(The) Caretakers

Randall, Terry - Katharine Hepburn in Stage Door

Sorry to take so long in responding, Lonesome Polecat, but I just moved and haven't had much access to the internet, much less the time to spend on it. Anyway, having said that, your answer is correct. Vera-Ellen "sang" (was dubbed, but I can't remember by who) and did an amazing dance to "So in Love" in the 1945 film Wonder Man. The thread is yours.

Hint: This song shares its title with a much more well known song by Cole Porter from Kiss Me Kate.

That is correct, KarmaGirl. Your thread.

I've got nothing right now. Thread's open.

No, I'm going to pass. Thread's open.

O'Leary, Jasper - David Niven in Tonight's the Night

Yvonne DeCarlo was in Tonight's the Night wit David Niven.

I'll See You in My Dreams

Pidgeon, Walter

Mander, Miles

Fanny

Jean Hagen was in Carbine Williams with Wendell Corey.

Law, Robert - James Cagney in Boy Meets Girl

My life motto is "Dignity, always dignity." (spoken by Gene Kelly in Singin' in the Rain) Actually I have 2 life mottos. The other one isn't from a movie, but from Shakespeare: To thine own self be true.

The Ghost and Mr. Chicken

That Certain Age of Consent

A Scandal in Paris

Since this is a trick question, I take it that you are not referring to Edmund Gwenn, but to the drunken Santa Claus that he replaces in Macy's Thanksgiving Day parade. That would be Percy Helton.

Claire Trevor was in Born to Kill with Walter Slezak.